Similar to a Peeping Tom, a Shutter Sheldon is a creep who takes/obtains inappropriate photos of someone who is not aware of it. This can be done by incognito photography or by going through a person's personal photos and sending said photos to themselves for later viewing/use.
Also applicable as a verb.
Noun
Jonathan took pictures of a girl while she was changing, this makes him a Shutter Sheldon.
Verb
"Friends don't shutter sheldon their friends. That makes you an asshole."