The whole issue of cover art is fraught with controversy, partially because of differing opinions with respect to the intent of maintaining a cover art archive. I’ve tried to summarize my understanding in another thread, where I also suggest that the MusicBrainz brain trust provide some clarification with respect to intent.
If my understanding is correct, and the primary purpose of the CAA is to provide archival information (images) with respect to releases, then I believe that the images uploaded should be unaltered scans or pictures for releases on physical media. Obviously this does not apply to a digital release.
I also believe there is a place for high quality digital cover art suitable for tagging one’s music collection (such as one would find with a digital release). Unfortunately, there does not seem to be a place for this within the CAA portion of MusicBrainz.
I’ve been told by others that this digital cover art is more appropriately stored on sites such as fanart.tv, so I am no longer uploading it to the CAA. Until something changes or is clarified, I am now limiting my cover art uploads (for physical media releases) to unaltered scans showing information supporting my edits.