diff --git a/OGImage/OGImage.h b/OGImage/OGImage.h
index e3456d7..aca2077 100644
--- a/OGImage/OGImage.h
+++ b/OGImage/OGImage.h
@@ -25,17 +25,17 @@
 
 /**
  * Convenience method: This is equivalent to calling
- *    [ogimg addObserver:observer forKeyPath:@"image" options:NSKeyValueObservingOptionNew context:nil];
- *    [ogimg addObserver:observer forKeyPath:@"error" options:NSKeyValueObservingOptionNew context:nil];
+ *    [ogimg addObserver:observer forKeyPath:@"image" options:NSKeyValueObservingOptionNew context:context];
+ *    [ogimg addObserver:observer forKeyPath:@"error" options:NSKeyValueObservingOptionNew context:context];
  */
-- (void)addObserver:(NSObject *)observer;
+- (void)addObserver:(NSObject *)observer context:(void *)context;
 
 /**
  * Convenience method: This is equivalent to calling
- *    [ogimg removeObserver:observer forKeyPath:@"image"];
- *    [ogimg removeObserver:observer forKeyPath:@"error"];
+ *    [ogimg removeObserver:observer forKeyPath:@"image" context:context];
+ *    [ogimg removeObserver:observer forKeyPath:@"error" context:context];
  */
-- (void)removeObserver:(NSObject *)observer;
+- (void)removeObserver:(NSObject *)observer context:(void *)context;
 
 /**
  * Subclasses can override this method to perform caching, processing, etc., but
diff --git a/OGImage/OGImage.m b/OGImage/OGImage.m
index 43c14aa..cd8ce29 100644
--- a/OGImage/OGImage.m
+++ b/OGImage/OGImage.m
@@ -26,17 +26,17 @@ - (id)initWithURL:(NSURL *)url placeholderImage:(UIImage *)placeholderImage {
     return self;
 }
 
-- (void)addObserver:(NSObject *)observer {
-    [self addObserver:observer forKeyPath:@"image" options:NSKeyValueObservingOptionNew context:nil];
-    [self addObserver:observer forKeyPath:@"error" options:NSKeyValueObservingOptionNew context:nil];
+- (void)addObserver:(NSObject *)observer context:(void *)context {
+    [self addObserver:observer forKeyPath:@"image" options:NSKeyValueObservingOptionNew context:context];
+    [self addObserver:observer forKeyPath:@"error" options:NSKeyValueObservingOptionNew context:context];
 }
 
-- (void)removeObserver:(NSObject *)observer {
+- (void)removeObserver:(NSObject *)observer context:(void *)context {
     @try {
-        [self removeObserver:observer forKeyPath:@"image"];
+        [self removeObserver:observer forKeyPath:@"image" context:context];
     } @catch (NSException *e) {}
     @try {
-        [self removeObserver:observer forKeyPath:@"error"];
+        [self removeObserver:observer forKeyPath:@"error" context:context];
     } @catch (NSException *e) {}
 }
 
diff --git a/OGImage/OGScaledImage.h b/OGImage/OGScaledImage.h
index 5bcba27..7bd23a6 100644
--- a/OGImage/OGScaledImage.h
+++ b/OGImage/OGScaledImage.h
@@ -49,11 +49,11 @@
 /**
  * Equivalent to adding an observer for @"image", @"scaledImage", & @"error"
  */
-- (void)addObserver:(NSObject *)observer;
+- (void)addObserver:(NSObject *)observer context:(void *)context;
 /**
  * Equivalent to removing an observer for @"image", @"scaledImage", & @"error"
  */
-- (void)removeObserver:(NSObject *)observer;
+- (void)removeObserver:(NSObject *)observer context:(void *)context;
 
 /**
  * The scaled image—The inherited `image` property is set to the full-size image at `url`.
diff --git a/OGImage/OGScaledImage.m b/OGImage/OGScaledImage.m
index ca63879..9424332 100644
--- a/OGImage/OGScaledImage.m
+++ b/OGImage/OGScaledImage.m
@@ -73,14 +73,14 @@ - (id)initWithImage:(__OGImage *)image size:(CGSize)size cornerRadius:(CGFloat)c
     return self;
 }
 
-- (void)addObserver:(NSObject *)observer {
-    [super addObserver:observer];
-    [self addObserver:observer forKeyPath:@"scaledImage" options:NSKeyValueObservingOptionNew context:nil];
+- (void)addObserver:(NSObject *)observer context:(void *)context {
+    [super addObserver:observer context:context];
+    [self addObserver:observer forKeyPath:@"scaledImage" options:NSKeyValueObservingOptionNew context:context];
 }
 
-- (void)removeObserver:(NSObject *)observer {
-    [super removeObserver:observer];
-    [self removeObserver:observer forKeyPath:@"scaledImage"];
+- (void)removeObserver:(NSObject *)observer context:(void *)context {
+    [super removeObserver:observer context:context];
+    [self removeObserver:observer forKeyPath:@"scaledImage" context:context];
 }
 
 - (void)loadImageFromURL {
diff --git a/OGImageDemo/OGImageDemo/OGImageTableViewCell.m b/OGImageDemo/OGImageDemo/OGImageTableViewCell.m
index d08ff55..371c701 100644
--- a/OGImageDemo/OGImageDemo/OGImageTableViewCell.m
+++ b/OGImageDemo/OGImageDemo/OGImageTableViewCell.m
@@ -9,6 +9,8 @@
 #import "OGImageTableViewCell.h"
 #import "OGScaledImage.h"
 
+static NSString *KVOContext = @"OGImageTableViewCell observation";
+
 @implementation OGImageTableViewCell
 
 - (id)initWithStyle:(UITableViewCellStyle)style reuseIdentifier:(NSString *)reuseIdentifier {
@@ -25,13 +27,18 @@ - (void)setSelected:(BOOL)selected animated:(BOOL)animated {
 #pragma mark - KVO
 
 - (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
-    NSAssert(YES == [NSThread isMainThread], @"KVO fired on thread other than main...");
-    if ([keyPath isEqualToString:@"scaledImage"]) {
-        self.imageView.image = self.image.scaledImage;
-        self.textLabel.text = [[self.image.url path] lastPathComponent];
-        self.detailTextLabel.text = [NSString stringWithFormat:@"%.2f", self.image.loadTime];
-    } else if ([keyPath isEqualToString:@"error"]) {
-        
+    if( (void *)&KVOContext == context ) {
+        NSAssert(YES == [NSThread isMainThread], @"KVO fired on thread other than main...");
+        if ([keyPath isEqualToString:@"scaledImage"]) {
+            self.imageView.image = self.image.scaledImage;
+            self.textLabel.text = [[self.image.url path] lastPathComponent];
+            self.detailTextLabel.text = [NSString stringWithFormat:@"%.2f", self.image.loadTime];
+        } else if ([keyPath isEqualToString:@"error"]) {
+            
+        }
+    }
+    else {
+        [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
     }
 }
 
@@ -42,19 +49,19 @@ - (void)setImage:(OGScaledImage *)image {
      * When the cell's image is set, we want to first make sure we're no longer listening
      * for any KVO notifications on the cell's previous image.
      */
-    [_image removeObserver:self forKeyPath:@"error"];
-    [_image removeObserver:self forKeyPath:@"scaledImage"];
+    [_image removeObserver:self forKeyPath:@"error" context:&KVOContext];
+    [_image removeObserver:self forKeyPath:@"scaledImage" context:&KVOContext];
     _image = image;
     self.imageView.image = _image.scaledImage;
     self.textLabel.text = [[self.image.url path] lastPathComponent];
     self.detailTextLabel.text = NSLocalizedString(@"Loading", @"");
-    [_image addObserver:self forKeyPath:@"error" options:NSKeyValueObservingOptionNew context:nil];
-    [_image addObserver:self forKeyPath:@"scaledImage" options:NSKeyValueObservingOptionNew context:nil];
+    [_image addObserver:self forKeyPath:@"error" options:NSKeyValueObservingOptionNew context:&KVOContext];
+    [_image addObserver:self forKeyPath:@"scaledImage" options:NSKeyValueObservingOptionNew context:&KVOContext];
 }
 
 - (void)dealloc {
-    [_image removeObserver:self forKeyPath:@"error"];
-    [_image removeObserver:self forKeyPath:@"scaledImage"];
+    [_image removeObserver:self forKeyPath:@"error" context:&KVOContext];
+    [_image removeObserver:self forKeyPath:@"scaledImage" context:&KVOContext];
 }
 
 @end
diff --git a/OGImageDemo/OGImageTests/OGImageAssetsLibraryTests.m b/OGImageDemo/OGImageTests/OGImageAssetsLibraryTests.m
index 8d61b8f..0a71a11 100644
--- a/OGImageDemo/OGImageTests/OGImageAssetsLibraryTests.m
+++ b/OGImageDemo/OGImageTests/OGImageAssetsLibraryTests.m
@@ -12,6 +12,8 @@
 
 #import <AssetsLibrary/AssetsLibrary.h>
 
+static NSString *KVOContext = @"OGImageAssetsLibraryTests observation";
+
 static CGSize const OGExpectedSize = {1024.f, 768.f};
 
 @interface OGImageAssetsLibraryTests : GHAsyncTestCase
@@ -44,18 +46,23 @@ - (void)setUp {
 }
 
 - (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
-    if ([keyPath isEqualToString:@"image"]) {
-        OGCachedImage *image = (OGCachedImage *)object;
-        if (nil != image.image) {
-            GHAssertTrue(CGSizeEqualToSize(OGExpectedSize, image.image.size), @"Expected image of size %@, got %@", NSStringFromCGSize(OGExpectedSize), NSStringFromCGSize(image.image.size));
-            [self notify:kGHUnitWaitStatusSuccess];
-        } else {
+    if ((void *)&KVOContext == context) {
+        if ([keyPath isEqualToString:@"image"]) {
+            OGCachedImage *image = (OGCachedImage *)object;
+            if (nil != image.image) {
+                GHAssertTrue(CGSizeEqualToSize(OGExpectedSize, image.image.size), @"Expected image of size %@, got %@", NSStringFromCGSize(OGExpectedSize), NSStringFromCGSize(image.image.size));
+                [self notify:kGHUnitWaitStatusSuccess];
+            } else {
+                [self notify:kGHUnitWaitStatusFailure];
+            }
+        } else if ([keyPath isEqualToString:@"error"]) {
+            OGCachedImage *image = (OGCachedImage *)object;
+            GHFail(@"Got error loading OGCachedImage: %@", image.error);
             [self notify:kGHUnitWaitStatusFailure];
         }
-    } else if ([keyPath isEqualToString:@"error"]) {
-        OGCachedImage *image = (OGCachedImage *)object;
-        GHFail(@"Got error loading OGCachedImage: %@", image.error);
-        [self notify:kGHUnitWaitStatusFailure];
+    }
+    else {
+        [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
     }
 }
 
@@ -63,9 +70,9 @@ - (void)testAssetsLibrary {
     [self prepare];
     GHAssertNotNil(_assetURL, @"Expect _assetURL to be populated by setUp");
     OGCachedImage *image = [[OGCachedImage alloc] initWithURL:_assetURL key:nil];
-    [image addObserver:self];
+    [image addObserver:self context:&KVOContext];
     [self waitForStatus:kGHUnitWaitStatusSuccess timeout:10.];
-    [image removeObserver:self];
+    [image removeObserver:self context:&KVOContext];
 }
 
 @end
\ No newline at end of file
diff --git a/OGImageDemo/OGImageTests/OGImageAsyncTests.m b/OGImageDemo/OGImageTests/OGImageAsyncTests.m
index 302ab0c..3d64c9e 100644
--- a/OGImageDemo/OGImageTests/OGImageAsyncTests.m
+++ b/OGImageDemo/OGImageTests/OGImageAsyncTests.m
@@ -10,6 +10,8 @@
 #import "OGImage.h"
 #import "OGImageLoader.h"
 
+static NSString *KVOContext = @"OGImageAsyncTests observation";
+
 static NSString * const TEST_IMAGE_URL_STRING = @"http://easyquestion.net/thinkagain/wp-content/uploads/2009/05/james-bond.jpg";
 static NSString * const FAKE_IMAGE_URL_STRING = @"http://easyquestion.net/thinkagain/wp-content/uploads/2009/05/james00.jpg";
 static const CGSize TEST_IMAGE_SIZE = {317.f, 400.f};
@@ -22,26 +24,31 @@ @interface OGImage404Test : GHAsyncTestCase
 @implementation OGImage404Test
 
 - (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
-    NSAssert(YES == [NSThread isMainThread], @"Expected `observeValueForKeyPath` to only be called on main thread");
-    if ([keyPath isEqualToString:@"error"]) {
-        OGImage *image = (OGImage *)object;
-        GHTestLog(@"Error changed: %@", image.error);
-        if (OGImageLoadingError == image.error.code) {
-            // we expect a loading error here
-            [self notify:kGHUnitWaitStatusSuccess];
-        } else {
-            [self notify:kGHUnitWaitStatusFailure];
+    if ((void *)&KVOContext == context) {
+        NSAssert(YES == [NSThread isMainThread], @"Expected `observeValueForKeyPath` to only be called on main thread");
+        if ([keyPath isEqualToString:@"error"]) {
+            OGImage *image = (OGImage *)object;
+            GHTestLog(@"Error changed: %@", image.error);
+            if (OGImageLoadingError == image.error.code) {
+                // we expect a loading error here
+                [self notify:kGHUnitWaitStatusSuccess];
+            } else {
+                [self notify:kGHUnitWaitStatusFailure];
+            }
+            return;
         }
-        return;
+    }
+    else {
+      [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
     }
 }
 
 - (void)test404 {
     [self prepare];
     OGImage *image = [[OGImage alloc] initWithURL:[NSURL URLWithString:FAKE_IMAGE_URL_STRING]];
-    [image addObserver:self];
+    [image addObserver:self context:&KVOContext];
     [self waitForStatus:kGHUnitWaitStatusSuccess timeout:10.];
-    [image removeObserver:self];
+    [image removeObserver:self context:&KVOContext];
 }
 
 @end
@@ -54,27 +61,32 @@ @interface OGImageTest1 : GHAsyncTestCase
 
 @implementation OGImageTest1
 - (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
-    NSAssert(YES == [NSThread isMainThread], @"Expected `observeValueForKeyPath` to only be called on main thread");
-    if ([keyPath isEqualToString:@"image"]) {
-        OGImage *image = (OGImage *)object;
-        GHTestLog(@"Image loaded: %@ : %@", image.image, NSStringFromCGSize(image.image.size));
-        if (NO == CGSizeEqualToSize(image.image.size, TEST_IMAGE_SIZE)) {
-            [self notify:kGHUnitWaitStatusFailure];
-        } else {
-            [self notify:kGHUnitWaitStatusSuccess];
+    if ((void *)&KVOContext == context) {
+        NSAssert(YES == [NSThread isMainThread], @"Expected `observeValueForKeyPath` to only be called on main thread");
+        if ([keyPath isEqualToString:@"image"]) {
+            OGImage *image = (OGImage *)object;
+            GHTestLog(@"Image loaded: %@ : %@", image.image, NSStringFromCGSize(image.image.size));
+            if (NO == CGSizeEqualToSize(image.image.size, TEST_IMAGE_SIZE)) {
+                [self notify:kGHUnitWaitStatusFailure];
+            } else {
+                [self notify:kGHUnitWaitStatusSuccess];
+            }
+            return;
         }
-        return;
+        GHTestLog(@"Unexpected key change...");
+        [self notify:kGHUnitWaitStatusFailure];
+    }
+    else {
+        [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
     }
-    GHTestLog(@"Unexpected key change...");
-    [self notify:kGHUnitWaitStatusFailure];
 }
 
 - (void)testImageOne {
     [self prepare];
     OGImage *image = [[OGImage alloc] initWithURL:[NSURL URLWithString:TEST_IMAGE_URL_STRING]];
-    [image addObserver:self forKeyPath:@"image" options:NSKeyValueObservingOptionNew context:nil];
+    [image addObserver:self forKeyPath:@"image" options:NSKeyValueObservingOptionNew context:&KVOContext];
     [self waitForStatus:kGHUnitWaitStatusSuccess timeout:10.];
-    [image removeObserver:self forKeyPath:@"image"];
+    [image removeObserver:self forKeyPath:@"image" context:&KVOContext];
 }
 
 @end
diff --git a/OGImageDemo/OGImageTests/OGImageFileTests.m b/OGImageDemo/OGImageTests/OGImageFileTests.m
index 1ba5e30..32a6e64 100644
--- a/OGImageDemo/OGImageTests/OGImageFileTests.m
+++ b/OGImageDemo/OGImageTests/OGImageFileTests.m
@@ -10,6 +10,8 @@
 #import "OGCachedImage.h"
 #import "OGImageCache.h"
 
+static NSString *KVOContext = @"OGImageFileTests observation";
+
 static CGSize const OGExpectedSize = {1024.f, 768.f};
 
 @interface OGImageFileTests : GHAsyncTestCase
@@ -23,16 +25,21 @@ - (void)setUp {
 }
 
 - (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
-    if ([keyPath isEqualToString:@"image"]) {
-        OGCachedImage *image = (OGCachedImage *)object;
-        if (nil == image) {
+    if ((void *)&KVOContext == context) {
+        if ([keyPath isEqualToString:@"image"]) {
+            OGCachedImage *image = (OGCachedImage *)object;
+            if (nil == image) {
+                [self notify:kGHUnitWaitStatusFailure];
+            } else {
+                GHAssertTrue(CGSizeEqualToSize(OGExpectedSize, image.image.size), @"Expected image of size %@, got %@", NSStringFromCGSize(OGExpectedSize), NSStringFromCGSize(image.image.size));
+                [self notify:kGHUnitWaitStatusSuccess];
+            }
+        } else if ([keyPath isEqualToString:@"error"]) {
             [self notify:kGHUnitWaitStatusFailure];
-        } else {
-            GHAssertTrue(CGSizeEqualToSize(OGExpectedSize, image.image.size), @"Expected image of size %@, got %@", NSStringFromCGSize(OGExpectedSize), NSStringFromCGSize(image.image.size));
-            [self notify:kGHUnitWaitStatusSuccess];
         }
-    } else if ([keyPath isEqualToString:@"error"]) {
-        [self notify:kGHUnitWaitStatusFailure];
+    }
+    else {
+        [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
     }
 }
 
@@ -41,9 +48,9 @@ - (void)testFileURL {
     NSURL *imageURL = [[NSBundle mainBundle] URLForResource:@"Origami" withExtension:@"jpg"];
     GHAssertNotNil(imageURL, @"Couldn't get URL for test image");
     OGCachedImage *image = [[OGCachedImage alloc] initWithURL:imageURL key:nil];
-    [image addObserver:self];
+    [image addObserver:self context:&KVOContext];
     [self waitForStatus:kGHUnitWaitStatusSuccess timeout:10.];
-    [image removeObserver:self];
+    [image removeObserver:self context:&KVOContext];
 }
 
 @end
diff --git a/OGImageDemo/OGImageTests/OGImageIdempotentTests.m b/OGImageDemo/OGImageTests/OGImageIdempotentTests.m
index ea3c179..2ffe697 100644
--- a/OGImageDemo/OGImageTests/OGImageIdempotentTests.m
+++ b/OGImageDemo/OGImageTests/OGImageIdempotentTests.m
@@ -9,6 +9,8 @@
 #import "GHAsyncTestCase.h"
 #import "OGImage.h"
 
+static NSString *KVOContext = @"OGImageIdempotentTests observation";
+
 static NSString * const TEST_IMAGE_URL_STRING = @"http://easyquestion.net/thinkagain/wp-content/uploads/2009/05/james-bond.jpg";
 
 @interface OGImageIdempotentTests : GHAsyncTestCase {
@@ -23,13 +25,18 @@ @interface OGImageIdempotentTests : GHAsyncTestCase {
 @implementation OGImageIdempotentTests
 
 - (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
-    if (_image1 == object) {
-        _image1Loaded = YES;
-    } else if (_image2 == object) {
-        _image2Loaded = YES;
+    if ((void *)&KVOContext == context) {
+        if (_image1 == object) {
+            _image1Loaded = YES;
+        } else if (_image2 == object) {
+            _image2Loaded = YES;
+        }
+        if (_image1Loaded && _image2Loaded) {
+            [self notify:kGHUnitWaitStatusSuccess];
+        }
     }
-    if (_image1Loaded && _image2Loaded) {
-        [self notify:kGHUnitWaitStatusSuccess];
+    else {
+        [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
     }
 }
 
@@ -38,11 +45,11 @@ - (void)testIdempotent {
     // a single network request with notifications
     [self prepare];
     _image1 = [[OGImage alloc] initWithURL:[NSURL URLWithString:TEST_IMAGE_URL_STRING]];
-    [_image1 addObserver:self];
+    [_image1 addObserver:self context:&KVOContext];
     _image2 = [[OGImage alloc] initWithURL:[NSURL URLWithString:TEST_IMAGE_URL_STRING]];
-    [_image2 addObserver:self];
+    [_image2 addObserver:self context:&KVOContext];
     [self waitForStatus:kGHUnitWaitStatusSuccess timeout:15.f];
-    [_image1 removeObserver:self];
-    [_image2 removeObserver:self];
+    [_image1 removeObserver:self context:&KVOContext];
+    [_image2 removeObserver:self context:&KVOContext];
 }
 @end
diff --git a/OGImageDemo/OGImageTests/OGImageProcessingTests.m b/OGImageDemo/OGImageTests/OGImageProcessingTests.m
index 48c09f3..fa982e0 100644
--- a/OGImageDemo/OGImageTests/OGImageProcessingTests.m
+++ b/OGImageDemo/OGImageTests/OGImageProcessingTests.m
@@ -11,6 +11,8 @@
 #import "OGScaledImage.h"
 #import "OGImageCache.h"
 
+static NSString *KVOContext = @"OGImageProcessingTests observation";
+
 extern CGSize OGAspectFit(CGSize from, CGSize to);
 extern CGSize OGAspectFill(CGSize from, CGSize to, CGPoint *offset);
 
@@ -81,29 +83,34 @@ - (void)tearDown {
 }
 
 - (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
-    NSAssert(YES == [NSThread isMainThread], @"Expected `observeValueForKeyPath` to only be called on main thread");
-    if ([keyPath isEqualToString:@"scaledImage"]) {
-        OGScaledImage *image = (OGScaledImage *)object;
-        GHTestLog(@"Image loaded: %@ : %@", image.image, NSStringFromCGSize(image.image.size));
-        CGSize retinaSize = TEST_SCALE_SIZE;
-        retinaSize.width *= [UIScreen mainScreen].scale;
-        retinaSize.height *= [UIScreen mainScreen].scale;
-        CGSize expectedSize = OGAspectFit(TEST_IMAGE_SIZE, TEST_SCALE_SIZE);
-        if (NO == CGSizeEqualToSize(image.scaledImage.size, expectedSize)) {
-            [self notify:kGHUnitWaitStatusFailure];
-        } else {
-            [self notify:kGHUnitWaitStatusSuccess];
+    if ((void *)&KVOContext == context) {
+        NSAssert(YES == [NSThread isMainThread], @"Expected `observeValueForKeyPath` to only be called on main thread");
+        if ([keyPath isEqualToString:@"scaledImage"]) {
+            OGScaledImage *image = (OGScaledImage *)object;
+            GHTestLog(@"Image loaded: %@ : %@", image.image, NSStringFromCGSize(image.image.size));
+            CGSize retinaSize = TEST_SCALE_SIZE;
+            retinaSize.width *= [UIScreen mainScreen].scale;
+            retinaSize.height *= [UIScreen mainScreen].scale;
+            CGSize expectedSize = OGAspectFit(TEST_IMAGE_SIZE, TEST_SCALE_SIZE);
+            if (NO == CGSizeEqualToSize(image.scaledImage.size, expectedSize)) {
+                [self notify:kGHUnitWaitStatusFailure];
+            } else {
+                [self notify:kGHUnitWaitStatusSuccess];
+            }
+            return;
         }
-        return;
+    }
+    else {
+        [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
     }
 }
 
 - (void)testScaledImage1 {
     [self prepare];
     OGScaledImage *image = [[OGScaledImage alloc] initWithURL:[NSURL URLWithString:TEST_IMAGE_URL_STRING] size:TEST_SCALE_SIZE key:nil];
-    [image addObserver:self];
+    [image addObserver:self context:&KVOContext];
     [self waitForStatus:kGHUnitWaitStatusSuccess timeout:10.];
-    [image removeObserver:self];
+    [image removeObserver:self context:&KVOContext];
 }
 
 @end
diff --git a/README.md b/README.md
index b462547..63473a6 100644
--- a/README.md
+++ b/README.md
@@ -16,12 +16,12 @@ over HTTP in a simple, extensible interface.
     /*
      * This is shorthand for calling KVO methods for @"image", @"scaledImage", and @"error"
      */
-    [ogImage addObserver:self];
+    [ogImage addObserver:self context:&KVOContext];
 
     // check to see if the image loaded instantly (e.g., from cache)
     if (nil != ogImage.image) {
         // we already have an image, so do whatever we need with it, otherwise
-        // we'll be notified in `observeValueInKeyPath` whenever the image changes
+        // we'll be notified in `observeValueForKeyPath:ofObject:change:context:` whenever the image changes
         [self displayImage:ogImage.image];
         // ooh, we also got all the image's metadata! Sweet!
         NSDictionary *exifData = [ogImage.originalFileProperties valueForKey:kCGImagePropertyExifDictionary];
@@ -66,16 +66,21 @@ placeholder image to use until loading is complete with
 ...
 
 OGImage *image = [[OGImage alloc] initWithURL:[NSURL URLWithString:@"http://somedomain.com/someimage.jpg"]];
-[image addObserver:self];
+[image addObserver:self context:&KVOContext];
 
 ...
 
 - (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
-    if ([keyPath isEqualToString:@"image"]) {
-        // image was loaded!
-        ...
-    } else if ([keyPath isEqualToString:@"error"]) {
-        // error loading image
+    if ((void *)&KVOContext == context) {
+        if ([keyPath isEqualToString:@"image"]) {
+            // image was loaded!
+            ...
+        } else if ([keyPath isEqualToString:@"error"]) {
+            // error loading image
+        }
+    }
+    else {
+        [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
     }
 }
 ```
@@ -100,16 +105,20 @@ OGScaledImage *image = [[OGScaledImage alloc] initWithURL:imageURL size:scaledSi
  * Note that here we're interested in the `scaledImage` property, not the full-size `image`
  * property.
  */
-[image addObserver:self];
+[image addObserver:self context:&KVOContext];
 
 ...
 
 - (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
-    if ([keyPath isEqualToString:@"scaledImage"]) {
-        // image was loaded and scaled!
-        ...
-    } else if ([keyPath isEqualToString:@"error"]) {
-        // error loading image
+    if ((void *)&KVOContext == context) {
+        if ([keyPath isEqualToString:@"scaledImage"]) {
+            // image was loaded and scaled!
+            ...
+        } else if ([keyPath isEqualToString:@"error"]) {
+            // error loading image
+        }
+    else {
+        [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
     }
 }
 ```