Below is a picture of civil war generals from 1865, where one of the commanders wasn't there for the original shoot (bottom) and was later added into the composition (top).
Another example is through the below image of Stalin. He was known for removing enemies out of his photographs. On the right a commissar was later removed after falling out of Stalin's following. This reminds me of the dictatorship present in George Orwell's 1984, where passages of text from books and articles are continuously updated so as to present information in the favour of 'the party', rewriting history to be as they saw fit and beneficial. People were left (although not allowed) to question what is/was true, where on occasions their memory contrasted to the (supposed) written fact.
Some occasions are somewhat more innocent than others, with no real misleading intention. Whereas others take advantage of the naivety of the viewer and our trust in photography and the media. The following photo was virally spread through emails and online. The image combines two photographs one of a HH-60G Pave Hawk helicopter by Lance Cheung and the other of a Great White shark by Charles Maxwell. As can be determined by the background the helicopter was shot in front of Golden Gate Bridge, where Great White sharks are commonly (never) seen. Perhaps ironically the photo of the shark was actually taken in False Bay, South Africa.