This one is a pain, I did this recently. First make sure you are taking a photo of the Sim and not something else accidently, if your photography skill is low then most of the time you end up taking a photo of something other than your target. When I did this I called the Sim outside and took the photo of her there, that way there were less objects in the way that my Sim could accidently take photos of instead. Make sure the photo is called "A Sim in the area" and remove it from your camera, should work, did for me.