I remember hearing about something that had to do with coding in pictures. Like, every picture has its own "fingerprint" of sorts. But I forget what that "fingerprint" is called. Does anyone know what I'm talking about? And if you do, what exactly can it tell you about a picture?
Digital watermarking. It's used to "tag" a file to track its distribution, and can tell you if, for example, a website has stolen an image you made. It's not actually that common in pictures, since a normal watermark can in most cases do the same job just as well (plus it serves as a deterrent since it's actually visible). It's better known for its use in MP3 files by the RIAA to catch P2P users.
Thank you to both of you, but I don't think that's actually what I'm looking for. I was under the impression that every digital photograph taken has its own DNA of sorts. You could look into the metadata (I think it's called) and find what make of camera took the picture, when it was taken, and loads of other stuff. Digital watermarking is something that you do after the picture is taken. What I'm talking about is something that the picture has in it already. Like when you snap the picture, the data is embedded in it from the second you click the shutter button.
Ah, you mean EXIF data. That's just basic unencrypted metadata optionally written into JPEG images by cameras and/or editing software. It usually includes a timestamp, the camera model used to take the picture, possibly the name of the owner and in some cases a serial number. It's pretty much JPEG's equivalent of ID3 tags, meaning it's trivial to edit, so I wouldn't put much trust in it; the first thing any semi-competent thief will do is strip the EXIF data right out of your image and possibly replace it with fake data.
I think he means the noise signature. See this Instructable for more info: http://www.instructables.com/id/Avoiding-Camera-Noise-Signatures/
