Originally Posted by: Swooshiain 
You don't have to save the photo for it to register. As soon as you take the pic and get the "new car" notification, press B a couple of times to back out without saving.
I don't know if this is a PC vs Xbox thing, but on PC you can't back out, you have to wait an eternity for it to complete processing. All inputs are disabled while it's processing.
I think I've figured out the "no new cars in shot" thing. I think it's basing the detection on what is there at the time you take the photo, rather than the frozen scene that is captured. So you go into photo mode with a car filling the screen, but it has gone by the time you take the photo, so even though the car is filling your photo, it doesn't detect it as present. When you exit photo mode, the game has moved on, and the car is no longer there. This problem isn't present when you enter photo mode from a race, only when freeroaming.