Upload the revised image from the source is the best thing to do I think.
MD5 mismatches are images in Danbooru that were somehow revised by their artist from the original source creating a mismatch from the source here in Danbooru. MD5s are somehow coincidence since we never knew when will an artist will revised their works, just makes sure to upload the revised version and parenting it to the MD5 image here in Danbooru.
