Not sure, I've had this one for quite a while. But I usually change it when Rafa wins something big, so my guess was a picture of him winning the Davis Cup.
I think it was this one
One of the most underrated matches of recent years this one, imo. Great contest, truly befitting of a Davis Cup deciding rubber. Shame Del Potro wasn't fit enough at the time to extend it to 5 sets as he outplayed Rafa for large chunks of the match, but still a great effort. Rafa was his usual self, weathering the storm and coming through with his superior fitness and defense, not to mention some spectacualar shots from seemingly impossible positions.