The “first run” of a simple image editor has been in WordPress 2.9-rare for about two weeks. It lets the user crop, flip and rotate an image. It also has an option to scale the original (largest) image and to restore the originally uploaded version. There is a multi-step undo and redo support. Changes can be applied to all image sizes or only the thumbnail. The initial code is by Stephan Reiter author of the Scissors plugin.
Currently when saving an edited image all previous intermediate image sizes are kept and the meta data for them (filename, width, height) is moved to another postmeta field. This is necessary to avoid breaking any posts or pages where the image was inserted. The editing workflow (multi-undo, preview of each step) makes it unnecessary to edit an image more than once or twice, however if an image is edited 6-7 times the backup files would be 25-30.
There are couple of ways to avoid keeping unnecessary images, we could either track when an image was used in a post or a page, or we could have “standard” names for the intermediate image sizes. Tracking image use can be somehow problematic considering all the different ways content can be published in WordPress.
Renaming the resized images from [imagename]-150×100 to [imagename]-thumbnail, etc. seems the more viable option. This would also bring instant image updates in already published posts, however may also have some compatibility problems with plugins that expect the image size to be part of the filename.
Trac ticket for the image editor, suggestions and patches welcome