Pictures would add additional information on your identity: similar to providing information on your name, location, place and date of birth, they might help others in identifying you (and distinguishing from people with similar names). A picture of you (and your signature, which seems an interesting idea) might help at verifying people meet with the right ones (or have a document really issued by you) when meeting: whether this is a real world problem, might be subject of discussion.
Compare your OpenPGP key with "extended" identity information with a digital identity card/passport.
Anyway, the risks of doing so are rather obvious. There is no risk to the "technical" security of your key, signatures on your images are just further signatures, exactly the same as the ones on your other user identities. For sure, there is a risk of identity theft, though: as all other information on your person, these could be used to impersonate your identity. If you've already put your photo on social media accounts, and your signature to your CV you put online, those information are public anyway, and all you do is giving a statement "these are really my picture and signature".