All throughout both parks they have signs with photo ops that are recommended.
It also depends what kind of photos you're looking for. Popular photo spots include:
USF:
Jaws shark, BTTF Delorean, on the bridge that crosses from Jaws to BTTF with MIB in the background, with the cars of studio 54
IOA:
On any of the small bikes in POE, the bridge the Hulk goes under, the giant Wolverine, the Popeye statue, by the JP splashdown, by the spinosaurs, next to the sea griffon in Lost Continent