While reading Wikipedia's entry on "Forced Disappearance", it mentions the methods that different governments utilized, notably the Soviet Union, Nazi Germany and Argentina. (What brought me there in the first place was the featured article on Mordechai Vanunu.)
In a very Orwellian fashion, dissident individuals were erased from society overnight. In Argentina, they would "disappear" over the Atlantic Ocean, thrown from airplanes, with none of the bodies ever recovered. In Germany and it's occupied countries, Gestapo agents would arrest, and either kill them on the spot, or send them off to concentration spots.
But the Soviet Unions' "Great Purge" definitely takes the cake: not only was the dissident "disappeared" by cold murder or pressed in forced Gulag labor; books, records, and history books which mentioned them were recalled or rewritten; statues, paintings and pictures were airbrushed, altered or removed, and the government generally forbade the mention of the disappeared person.
As seen on here on Newseum, the commissar of water transport, one Mr. Nikolai Yezhov was airbrushed out of existence. There are also a few more interesting examples of retouched photos on the site to view.