Please see https://www.mediawiki.org/wiki/Extension:Html2Wiki

Options:

$wgH2WEliminateDuplicateImages boolean false - when set to true, imported image (and their references) will be flattened to [CollectionName/]image.jpg instead of [CollectionName/]nested/folder/image.jpg thus eliminating duplicates based on repeated nested folders $wgH2WProcessImages boolean true - when set to false, image processing will be skipped, saving time in the re-upload of content when no images have changed. With a simple preference option, we avoid doing a binary diff on every image. @todo create preference element in form