It's true it's not required, but when it's requested because multiple people say they've seen the pics before, it would be good form to comply.
Sorry if it seems we're jumping on you, but we have had a rash of people faking lately it seems.
Also, you should see the problem in your own words... "unless they have been lifted." Those places you posted are not the least bit secure. Anyone could DL those pics and pose as the guy or girl and claim to be them. Would you want someone else doing that?
A verified pic does NOT have to be sexual in nature, it could even be fully clothed (and the before/after freaks among us would love that). All we want to see is that the woman holding an FF sign is the same as in the sexy pics, which also proves she is both aware of the pics being taken and giving consent to them being posted here.