The problem is very prolific and I think just about everyone has had it. To find the photos though, the search feature at the top of the page would have helped you find the answer sooner, but to find the photos go to
Start > All Programs > Microsoft Games > Zoo Tycoon 2 > Zoo Tycoon 2 Profiles
click Default or your profile name
then Photos. Click through till you find the right one.
In any event just mess with the graphics settings really quick and then it should help it.