With Masking->image, the region of interest corresponds to positive pixels in image.
Masking->array operates on regions corresponding to positive values in array.
When the region of interest is specified as an array or image, it is taken to be centered on the image to be processed.
Masking->graphics rasterizes arbitrary graphics to the size of the image to be processed, and operates on regions that correspond to positive values in the raster.
EXAMPLES
Basic Examples 
