Since the image code once loaded is just a stripe of pixels in a row, you can put any part of the image you want as long as its a column of images. Imagine a image 3x3 pixels large. The pixels would be numbered:
0 1 2
3 4 5
7 8 9
When you load an image it returns a pointer which tells where in the memory the image is stored. So you could use this pointer + the pixel number to show only part of the image. If you ie want to show only the two bottom lines, you could use:
CopySprite(x,y,3,2,pointer+3)
And the image would look like:
3 4 5
6 7 8

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Spoon.