Lucas Levitan, a Brazilian artist living in London, calls his project Photo Invasion. He takes other people's Instagram photos and edits them by adding new characters and challenges. They're delightfully subversive at times.
(Content warning on both links above: occasional gore and nudity.)
In an interview about his work, Levitan explained that his project expresses that no work of art is truly finished:
By interfering with their images it makes them think about what they’ve created not as a finished project, but something that sparks off other peoples’ understanding. Create a new narrative and a new story line.
-via 123 Inspiration