Digitial photography brought photo manipulation within the reach of anyone with a computer. Not to mention lots of free publicity for Adobe’s Photoshop, as in the term photoshopping.
New ways to detect photoshopping are being developed.
Abstract:
We describe a geometric technique to detect physically inconsistent arrangements of shadows in an image. This technique combines multiple constraints from cast and attached shadows to constrain the projected location of a point light source. The consistency of the shadows is posed as a linear programming problem. A feasible solution indicates that the collection of shadows is physically plausible, while a failure to find a solution provides evidence of photo tampering. (Eric Kee, James F. O’Brien, and Hany Farid. “Exposing Photo Manipulation with Inconsistent Shadows“. ACM Transactions on Graphics, 32(4):28:1–12, September 2013. Presented at SIGGRAPH 2013.)
If your experience has been with “photoshopped” images of political candidates and obvious “gag” photos, consider that photo manipulation has a darker side:
Recent advances in computational photography, computer vision, and computer graphics allow for the creation of visually compelling photographic fakes. The resulting undermining of trust in photographs impacts law enforcement, national security, the media, advertising, e-commerce, and more. The nascent field of photo forensics has emerged to help restore some trust in digital photographs [Farid 2009] (from the introduction)
Beyond simple provenance, it could be useful to establish and associate with a photograph, analysis that supports its authenticity.
Exposing Photo Manipulation with Inconsistent Shadows. Webpage with extra resources.
In case you had doubts, the technique is used by the authors to prove the Apollo lunar landing photo is not a fake.
PS: If images are now easy to use to misrepresent information, how much easier is it for textual data to be manipulated?
Thinking of those click-boxes, “yes, I agree to the terms of ….” on most websites.