There are plenty of places to watch online video, but still no easy way to find a particular clip without suffering through a lot of trial and error. Now a startup led by a former Yahoo engineer is promising to simplify Internet video search with a complex technology that enables computers to recognize images, such as actors’ faces, and index them scene-by-scene. “We absolutely think that it’s a leap forward in finding and discovering video on the Web,” said Lior Delgo, who left Yahoo in 2006 to start VideoSurf.