@lateinautumn , thank you for contributing to MusicBrainz. I see you have made thousands of edits in just one year. That is fantastic!
That said: no, I think uploading product photos from retailers as if they were actual artwork is not acceptable.
Why? Because the retailers are not reliable sources: they can be pretty sloppy in what they put up, they just want to sell goods, they are not trying to make the accurate database that we are. And because an image of one Release, accurate or not, is not applicable to another Release of the same Release group. A cover image of a CD Release should be a picture of the physical CD’s cover, not the artwork included with a similar MP3 digital download.
So, if you have the physical CD, then scan the front cover and upload that. If you don’t have the physical CD, then you are not in a position to provide cover art for that CD Release entry. If you have the MP3 digital download, you are in a position to extract the artwork embedded in that file and upload it as the cover for the digital media Release. If you do not have the digital download, then you are not in a position to provide the cover art for that digital media Release. If you can’t provide cover art, leave it empty, and let someone later fill in that gap.
I understand the appeal of providing an approximately similar cover art image where there is none, so that Release listings have pretty pictures, and media files on music players have a nice visualisation. But the project needs to make a decision about how similar is “similar enough”. I understand the MusicBrainz guidelines to say, sales-oriented artwork from unreliable retailers is not similar enough for the database we are making.
What are workarounds? The MusicBrainz system can find alternative images to fill in blank entries, without that alternative being labelled as the real thing. For a while, the MusicBrainz system used Amazon preview images in this way. And, anyone using Picard to tag music files can supply their own cover art image to Picard, even if that image is not really of the Release being tagged.
Do you see the logic of this standard?