There have been been devices on the market that detect lenses for some time , but a system was recently prototyped that is, to my knowledge, the first that goes beyond simple detection and actively counters the operation of at least some digital camera systems.
(Disclosure: my company markets a Russian-manufactured device that detects optics.)
Engineers at the Georgia Institute of Technology have prototyped a system to automatically detect and temporarily blind the image sensors used in digital cameras. Detection is accomplished by exploiting a characteristic of digital image sensors - by their nature, they reflect light back to the source (i.e. retroreflection).
Automatically finding reflections isn't all that difficult, but then you have to filter out the false positives (reflections which aren't really from camera sensors) and guide beams of light at the remaining reflectors. This article describes some general details of the method.
Proposed uses include thwarting people making pirated videos in cinemas, paedophiles making videos of children visiting shopping mall Santas, espionage in government buildings, and so on. The technique will not work against still image cameras that use a shutter to shield the sensor until a picture is taken, which includes some digital cameras and all film cameras.
(Hat tip: Digg)