Are you looking at a digital photo in its raw, original state — or has it been edited? Under normal circumstances this can be very hard to determine. But if you really need to know JPEGSnoop may be able to help. Just open your image and the program will examine its compression characteristics, compare these against a database of thousands of cameras and photo editors, and deliver its verdict.
So if your image matches the signature of a camera, it’s probably an original shot; if it matches a photo editor, it probably has been edited, or at least saved in an editor; and if the signature isn’t recognized then JPEGSnoop won’t be able to say (though you can add signatures to the database manually to improve its accuracy).
If you’d like more information on the image, then scroll back through the JPEGSnoop report. It’s packed with low-level JPEG technicalities, but if you skip past the quantization table and Huffman codes then you’ll also find more immediately useful nuggets, like the file’s EXIF data. These are tags that are sometimes embedded in the image by a digital camera, and might tell you when the photo was taken, perhaps where, the camera that was used, and more.
The program can also be used to grab JPEG images from any file that might embed them: PDF documents, THM (thumbnail) files, digital negatives, even AVI videos if they use Motion JPEG compression. Simply open the file, keep clicking Tools > Image Search Fwd, and JPEGSnoop will scan your document’s innards looking for JPEG signatures. You’ll then be able to extract anything it finds as a stand-alone JPEG file. And while you could, say, take a screen grab of a PDF and extract the image that way, this may be preferable as there’s no re-encoding involved, no further loss of image quality.
And if you’ve a JPEG image that’s corrupted and can no longer be viewed, then JPEGSnoop may be able to help by at least recovering the photo thumbnail (assuming there is one). Just open the picture, see what the program can uncover, and if you’re in luck, use the Tools > Export JPEG option to save your thumbnail as a stand-alone image.