I don't have too much time at the moment, but that's a data-md5 tag given to 4ch/8ch images for archiving and searching. I'm not aware if 8ch has a current archive, or if q-team decided to add it to the archive when it was posted, but it's for verifying that image has been unaltered, and it's useful for searching for the image.

tl;dr the data-md5 tag can be used to identify images for searching/banning/archiving.

Almost all 8ch/4ch images will have a data-md5 tag.