Heart Gold and Soul Silver: Commemorative Photos
After you beat Whitney in Goldenrod City to get the Plain Badge a man named Cameron can be found throughout both Kanto and Johto to take your picture with your party Pokemon. He will also take your picture with Gym Leaders if you call them on specific days. The pictures you take will be viewable in your PC and you can have up to a total of 36 photos.
A question often asked: "Is there a point to these photos?" No, there really isn't any point to getting your photo taken. There isn't a reward for finding all of the places to take a photo.