How does continuous computer vision works?
It depends on what you're recognizing, but I'm familiar with two basic techniques:


Apply the recognition algorithm to each frame of the video.  Be fast enough that you can run on every frame of video.  This is probably the most common approach.
Recognize the object once, in one frame.  Then use motion tracking to keep track of the location of the object in subsequent frames.  In this way, you might be able to run the recognition algorithm (say) once every 10 frames and then use motion tracking to keep track of where it is in the remaining frames.  This has some tradeoffs (some latency to detect the object when it first occurs; fast motion or fast panning can cause loss of the object), but is another possible alternative.