Region Capture is a very useful tool for capturing changing images on your desktop, a web cam window for instance.

The Region Capture window is a transparent window you place over  the region of the desktop you wish to capture.  This can be the desktop or another open window displaying an image of some kind.  Click the "Camera" icon and what ever the window is over, is captured as a JPG image in the current directory that ImageView is open at.

For images that are changing, such as a camera window, you can use the "Continuous" check box along with the "Seconds" field to capture images on a preset interval.  The "Compare" option will compare the current image with the image just captured, if they are different and new image is captured, otherwise it will be discarded.

Please note that this method does not work with all types of windows.  Most multimedia windows (DirectX) cannot be captured in this manner due to the way they are rendered to the screen, however most standard and web windows will work.