Blowup (1966)

A successful mod photographer in London whose world is bounded by fashion, pop music, marijuana, and easy sex, feels his life is boring and despairing. Then he meets a mysterious beauty, and also notices something frightfully suspicious on one of his photographs of her taken in a park. The fact that he may have photographed a murder does not occur to him until he studies and then blows up his negatives, uncovering details, blowing up smaller and smaller elements, and finally putting the puzzle together.