Every picture in public/images, with the pages that use it. Read from thebuilt site, not from the source files, so a picture that no page renders really is unused — and one nothing points at is safe to archive. Pick a picture to see every page that points at it, swap in a new one, or archive it. Tags are worked out automatically from the folder, the filename, the alt text and the pages each picture appears on; you can take any picture's tags over and hand them back again.
Nothing here deletes a file. Archiving stops a picture shipping with the site but leaves it in the repository, and replacing one leaves the original where it is — so both undo in a click.