For the images that come from FurAffinity, the artist is part of the file name -- if the name is '1234567890.xyz_abcde.jpg', the number is a sequencing value FA attaches (so a user can upload two files with the same name, and FA will keep them separate), 'abc' is the FA member's account name, and 'abcde' is the name the file had on the user's computer when they uploaded it.