How can I detect the movement of an rectangle in an image-stream efficiently?

I'd like to fi开发者_运维知识库nd an algorithm that can detect the movement (and movement-vector) of a rectangular area -- like scrolling a window would produce -- in an image-stream. Any ideas? :)

---

Optical Flow's idea should work, but it depends on the type of features you have in the window (images, text), and whether they're unique enough to be matched reliably in subsequence frames.

RANSAC is a method of given two images, it would compute the homography affine transformation from one image to the other, given that the features matched between them are mostly matched correctly