Secret photography refers to the use of an image or video recording device to photograph or film a person who is unaware that they are being intentionally photographed or filmed. It is sometimes called covert photography.
Sometimes normal cameras are used, but the photographer is concealed. Sometimes the camera itself is disguised or concealed. Some obvious element of concealment (or great distance) is generally needed to make such photography fall under the category of ‘secret photography’ rather than street photography or documentary photography.
It has been in use by British police since intelligence gathering on the suffragette movement in the 1900s. Erich Salomon took images of European summit meetings and a session of the US Supreme Court in secret using an Ermanox camera hidden in his hat. Some classic early U.S. street photography – such as that of Paul Strand on the Lower East Side – was obtained by fixing a second “dummy lens” to the camera, whereas the real shot was taken from the side. Although spy cameras small enough to fit inside a pocket watch had existed since the 1880s, since the 1950s advances in miniaturisation and electronics has greatly aided the ability to conceal miniature cameras, and the quality and affordability of tiny cameras (often called “spy cameras” or subminiature cameras) has now greatly increased. Some consumer compact digital cameras are now so small that in previous decades they would have qualified as “spy cameras”, and digital cameras of 41 megapixels are now being embedded in some mobile camera phones. For larger cameras (DSLR or EVIL), right-angle mirror attachments are commercially available that, when mounted on long-focus lenses, can deceive the subject by producing the impression that the camera is pointed in a different direction.