I’ve mentioned about Exif metadata in the past two posts, EXIF viewer reveal complete hidden info for any Photo and How to removes all EXIF data from all images.
JPEGSnoop is a free Windows utility that determines if the image has been altered or edited. It starts by reading a JPEG/JPG file’s EXIF data to give you a lot of information about the photo: time it was taken, what kind of camera, lens settings, and so forth. It also provides a load of additional information including details on the type of editing program used and the quality level the edited JPEG image was saved as. You’ll see a lot of gibberish data in the report, scroll down completely to see some actual information.
Then it compares the compression patterns in the image against the patterns of known image editing applications. The application can open various file types that contains an embedded JPEG image like: ..JPG,.THM, .AVI, .DNG, .CRW, .CR2, .NEF, .ORF, .PEF, .MOV, .QTVR, .PDF
The drawback with this is, it considers the image as edited even if the photo is cropped and resized and not major changed done. Download JPEGSnoop here.