We can't say for sure whether this was the first hidden camera stunt, but it goes pretty far back. Nineteen-year-old Norwegian math student Carl Størmer bought a small camera and surreptitiously took photos of people on the main street in Oslo from 1893 to 1897.
In his biography for the Fellows of the Royal Society, he revealed it was actually a secret crush that led him toward photography. “When he was a young man at Oslo University he fell in love with a lady whom he did not know and with whom he was too bashful to become acquainted,” writes his biographer. “Wishing at least to have a picture of her, he decided that this was possible only by taking a photograph of her himself, without her knowing.”
The candid shots from the streets of Oslo are much more revealing than the portraits of the era. Around 500 of Størmer's photograph's were later exhibited when he was in his 70s. See a selection of them at My Modern Met. -via Boing Boing