Ultimately, you have to trust some photographer or organisation. The camera sensor is not a trusted input. Nothing can prevent somebody pointing their camera a

Ultimately, you have to trust some photographer or organisation. The camera sensor is not a trusted input. Nothing can prevent somebody pointing their camera at a high resolution screen displaying a manipulated image. Or a staged scene. No image signing mechanism can prevent this kind of attack. There are manipulation detection techniques, but they are imperfect. And even if you verify the image is an unmodified camera original, you still have to analyse the context surrounding the image (what is portrayed in the image, does it line up with other reports, who is the photographer etc.) to determine if it is actually a true. It is trivial to digitally sign text, but a signature on a string doesn't mean that string is telling the truth. It just means someone signed it. Highly recommend http://www.hackerfactor.com/blog/ http://www.hackerfactor.com/blog/ for in depth digital image forensics content.