Upon saving Doc from Irving "Kid" Tannen on June 13, 1931, Marty felt himself erasing from existence. After finding out that giving his grandfather Arthur McFly resulted in his premature death, Marty looked at the photo of George to find him slowly disappearing. After traveling back in time to 6 hours ago in the same day, Marty took out the photo several times to see if he succeeded in saving Arthur.
On August 25 of the same year, Marty needed to convince Trixie Trotter that Kid went back on his word to kill Arthur. To do so, he gave Zane Williams the photo of George to make a caricature sketch, with the addition of a hat, which resembled Arthur. Afterwards, Marty placed the sketch on the Wall of Fame to deceive Trixie.
The next day, while in the Citizen Plus ward, Marty told George (who hacked into the intercom) about his possessions being locked up. George used a camera recording of the guard opening the locker, and was thus able to reopen it so that Marty could get his possessions out, including his guitar and photo.