Of course, it's a hint for you to put up the photo.
Although not having a photo of her alone is not that big a deal, to me, if she's in the other photos. That is a little narcissistic, I think.
Many churches, when putting together their photo directories of members, will allow the photographer to offer a "free" large photo of the member just for coming in and having their pics taken. We have photos of both sets of parents from that kind of situation.
I don't consider photos of oneself to be an appropriate if that's the only gift, unless they are from elderly relatives (who judging from the comments I received when signing up people for our church directory, hate having their photos taken. Golly!)
I think they make lovely "additional" gifts...but just a portrait of oneself, "Here's you, looking at me!" has just never seemed like the most thoughtful of gifts.
My favorite e-hell oriented BIL once brought all the proofs of his daughter from a professional sitting, so we could order at will (and our own cost.)