To use the add-on, select your cards in the Browse screen, and use the 'Localize Images' option in the Notes menu. The add-on will scan your cards for any remote media links and inlined images, eg:
<img src="http://example.com/image.jpg">
<img src="data:image/jpeg;base64, .....">
[sound:http://example.com/file.mp3]
If any are detected, the remote links will be downloaded, and the references converted into local references like [sound:file.mp3] instead.
If you encounter an error while downloading, you can repeat the operation and previously localized notes will not need to be localized again.
Updated 11 Apr 2023 to support recent Anki versions and provide better progress.
Updated 26 Nov 2018 to support downloading audio files as well.
Updated 20 Aug 2018 to support converting inlined images into files in the media folder.
Updated 23 Apr 2018 to fix the action triggering on other browser commands.