“A new forensic technique means many digital photographs can now be traced to the individual cameras that took them. The method works by analysing imperfections in the cameras’ light sensors. […]
The technique can even trace digital images that have been compressed or cropped: “We tried all the stuff that people normally do with digital images, and found it was resistant,” [Jessica Fridrich at Binghamton University] told New Scientist.
But she admits that extensive testing will be needed to determine precisely how accurate the process is, and what the chances of an error are.”