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zero-shot-captcha-solver

A zero-shot captcha solver built on top of the multi-modal vision and language model CLIP and hosted in a Streamlit application. It is zero-shot as it does not require showing any labelled examples but works out of the box for arbitrary captcha images.

1. Task Description

Given a captcha image like the one below and an object to look out for - "chimney" in this case - the goal is to classify each individual image in the 3x3 grid into either being a hit (and therefore containg the object) or not.

2. Implementation Details

Below is a list of steps that the application follows:

  1. Turn single image of 3x3 images into 9 individual images
  2. Compute an embedding vector for each of the 9 individual images, and one single embedding vector for the object to search out for
  3. Compute the pairwise cosine-similarity between the embedding of each of the 9 images and the text embedding
  4. Cluster the thereby returned similarity scores - one for each image - into "match" or "no match"
    • sort the similarity scores and corresponding images in an ascending order
    • compute the differences between the current and the next element in this sorted list
    • find the largest difference/gap in similarity scores and use that gap to classify all images below as "no match" and all images above as "match"

3. Demo

Currently there are two demos.

3.1 Streamlit application

I wrapped this project into a streamlit application and hosted it on their servers: https://zero-shot-captcha-solver.streamlit.app/

3.2 Jupyter Notebook

Find a notebook that runs through the code at the example of one captcha image at demo.ipynb.

4. How to Install

There are two ways to install the required dependencies and run the code locally:

4.1 With poetry

This will install zero-shot-captcha-solver as a library within the virtual poetry environment.

  1. Clone the repository
  2. Install poetry
  3. From the root of the repository, install zero-shot-captcha-solver by executing poetry install

4.2 Without poetry

This won't install zero-shot-captcha-solver as a library.

  1. Clone the repository
  2. Install the (dev) requirements with pip install -r requirements(-dev).txt

5. Special Thanks

Special thanks to:

  • The whole Streamlit team for allowing to host streamlit applications for free on their infrastructures.

6. License

The code itself is licenced under the MIT License.