I am 5'2''.
I always respond with "I am Luke Skywalker, and I am here to save you Princess" as I point to them.
Once they realize I am a girl, they start laughing and apologize.
As far as those comments go on pictures... I always say that whoever is pictures with me is abnormally tall and I am of average height.... Yeah, that Jawa, shes actually 6ft, so of course we look the same size ;-)