A lot of images on the web come with an ‘alt’ attribute, that specifies an alternate text in case the image cannot be displayed; this attribute gets lost upon pasting into Anki.
I think it would be quite useful if it was kept instead.
e.g.
it would be helpful when media synchronization upon multiple devices is yet to be completed or encountered some errors
it often contains infos about the image source
it would add some keywords to the image, which could then be used when searching the browser
Also, the ‘alt’ attribute usually comprises just a few words, so, as far as I understand, it should not ‘weigh’ much on disk space, memory etc.