Picture Frames are collectibles in all three Ty the Tasmanian Tiger games.
In Ty 1, there are 250 picture frames, with 123 of them hidden in the Bonus World. In Ty 2, there are 175. And in Ty 3, there are 120. Picture Frames are usually hidden inside invisible crates, though sometimes they can be found out in the open. Collecting a Picture Frame awards the player with bonus concept art found under Main Menu > Extras > Gallery in Ty 1, or Main Menu > Extras > Concept Art in Ty 2 and 3. You can only do this after you load a save file with at least one Picture Frame.