I am wondering how (if) I can reuse a cover image that already exists at coverartarchive.org.
I feel that this is a common use case in release groups where you have multiple versions of release sharing the same cover art. Nevertheless, I did not figure out how to achieve this. The only way I am aware of is downloading an image from coverartarchive.org to my computer in order to upload it again through the “Add cover art” button via musicbrainz.org. Is it really desired to store multiple copies of the same cover art images at coverartarchive.org …or did I miss something?
You didn’t miss anything, it is just not possible at the moment.
By the way, you don’t have to download the images first before you upload them again. At least in Windows, you can copy the URL and paste it in the file picker in the file name field when you add an image to a release.
In theory, the images shouldn’t be the same. Of course, there might be some cases where they are; for example the front cover (but not the back cover) of two different CD versions. But if it makes it harder for people to submit some random image from Google to all versions of a release without caring whether it fits properly, I’d say it’s worth the slightly increased workload for the cases where this is legitimate.
There are plenty of cases where this is not true, different versions of the same release often share the same cover. Sometimes even the entire booklet. The cover art is just as same as it is between different copies of the same release.