My wife's nephew has a 3 year old son of whom the kid's grandmother has taken a zillion photos. On a trip to the beach last summer Nana was being her usual paparazzi-self. Upon leaving one store mom noticed that the boy did not have his hat on. By looking thru all of Nana's photos they figured out in which store and where in the store he had left the hat.

The hat was recovered and the day saved.

Darn good idea in the OP.

Andy