Fourandsix Technologies launched izitru.com (= “is it true”), a free service that claims to be able to spot whether an image has been post-processed or not.
You can upload an JPEG image file and let the algorithm run various analysis tasks to decide if the picture has been manipulated. If the image was not processed, Izitru gives the image a “trust” rating. Can be useful on social media, for business etc. About how the algorithm spots processed images:
There are a variety of ways in which an original JPEG file, as first saved by a digital camera, may be different from subsequent versions of the file. Some of these differences reflect the fact that each digital camera has distinct ways of applying JPEG settings when saving a file. Other differences result from artifacts that are introduced when images are saved multiple times. We use a combination of six distinct forensic tests to look for these differences.
Recently I found a paper about another algorithm, this time to measure the popularity of a photo (you can try it out).[via DPreview]