"Unlogo is a web service that eliminates logos and other corporate signage from videos." An art project by Jeff Crouse, it is, technically speaking, "an FFMPEG AVFilter that attempts to block out corporate logos using OpenCV 2.1 and an awesome 'plugin' framework for FFMPEG." Unlogo is open sourced; its code-in-progress is available here.
The artist also talks about an iPhone app that "can be used by individuals to identify logos that may occur in photographs they take with their phone and to replace them with images drawn from an online databank."
A Kickstarter campaign was organized to support the project, but it fell short of the $4,000 target.