i've long been a great admirer of ukrainian photographer boris mikhailov's work (i even wrote an article about him for the encyclopedia of 20th century photography). these are all from a series of superimposed photographs he started back in the '60s when he lived under a strict soviet regime, and the rules that governed art certainly did not allow for work like this. you can take a peek at more from boris' sandwich series here. and read stuff about him here.
[all boris mikhailov. superimposition. 1965.]