Find known sub image in larger image

Question

Does anyone know of an algorithm (or search terms / descriptions) to locate a known image within a larger image?

e.g.

I have an image of a single desktop window containing various buttons and areas (target). I also have code to capture a screen shot of the current desktop. I would like an algorithm that will help me find the target image within the larger desktop image (what exact x and y coordinates the window is located at). The target image may be located anywhere in the larger image and may not be 100% exactly the same (very similar but not exact possibly b/c of OS display differences)

Does anyone know of such an algorithm or class of algorithms?

I have found various image segmentation and computer vision algorithms but they seem geared to "fuzzy" classification of regions and not locating a specific image within another.

** My goal is to create a framework that, given some seed target images, can find "look" at the desktop, find the target area and "watch" it for changes. **