Most pictures that get uploaded on other sites are usually found by fans and are then posted on here, but you could always try places like Tumblr, Photobucket, ect.
If you're starting to collect pictures, I'll start you off! ;-)
I think that the best way to find loads an nice Johnny Depp's pictures is to search in Google (Images) "Johnny Depp",and you'll find his best pictures all together!