In the 1970s, Japanese photograhper Kohei Yoshiyuki stumbled upon a couple in a park engaged in sexual activity in the darkness and, somewhat more curiously, two men creeping towards the couple, watching them. Over many months, he followed these voyeurs in the park, befriended them, and outfitted his camera with an infrared flash so as to blend into the crowded darkness. The result is a fantastic series of photos called The Park. As you can see in the photo below, Yoshiyuki even caught some of the peeping toms touching their "visual prey".
Yoshiyuki's photographs explore the boundaries of privacy, an increasingly rare commodity. Ironically, we may reluctantly accommodate ourselves to being watched at the A.T.M., the airport, in stores, but our appetite for observing people in extremely personal circumstances doesn't seem to wane.
The NY Times has an audio slideshow of some images from The Park, which is on display at the Yossi Milo gallery in NYC until October 20 (more photos). A book of Yoshiyuki's photography is available at Amazon.
The Times article mentions several photographers whose work is similar to Yoshiyuki's. Merry Alpern took photographs through a window of prostitutes plying their trade with Wall Street businessmen. Weegee used an infrared flash to capture kissing couples at the movie theater (although it seems that particular shot was staged) and on the beach at Coney Island (last photo here). Walker Evans photographed people on the subway without their knowledge.