Returns the number of bytes required to store a rectangular region of the screen.
function ImageSize(x1, y1, x2, y2: Integer): Word;
X1, Y1, X2, and Y2 define a rectangular region on the screen. ImageSize determines the number of bytes necessary for GetImage to save the specified region of the screen. The image size includes space for three words. The first stores the width of the region, the second stores the height, and the third is reserved.
If the memory required to save the region is greater than or equal to 64K, a value of 0 is returned and GraphResult returns -11 (grError).
Must be in graphics mode.