I want to be able to capture the background and then manipulate a piece of that image. For example, take a square of 50 pixels in the middle of the background and then rotate it. I know that I can use captureScreen to get the background into an object and use other display functions to rotate and scale. But how do I cut out only the part of the image that I need?

how about using a mask?

Thanks for the suggestion but that's not the effect I'm going for. I want to take a section of the screen, like a circle at some variable coordinates, and turn it into a display object, all the while leaving the screen intact, including the area that was turned into the circle. I then want to move the new display object around the screen, rotating it as it moves.

the output of display.captureScreen( ) is a display object and as such it can be masked
put it in a group and mask the group with a circle at maskX,maskY
then, move and rotate the group
the screen is not affected