If you have open edits for an image, and then you remove the image, cancel the add edit or vote down the add edit, the open edits now have broken images. One way to reproduce it:

• add cover art - http://test.musicbrainz.org/edit/16086327
• remove cover art - http://test.musicbrainz.org/edit/16086330
• cancel first edit

Result: Second edit has a broken image

The best solution would be to make any open edits for an image fail if that image is removed. If that's not possible without a lot more work, then I think we should display a message saying the image can't be shown (I assume it's possible, since we already detect images where the thumbnail doesn't load).