image.crop(src,dst,x1,y1,x2,y2)
crops the Tensor src
by taking only the part of the image with top left-hand
corner (x1,y1) and bottom right corner (x2,y2)
to fit the destination Tensor dst.
If dst is not of size (x2-x1+1,y2-y1+1) then the cropped
part of the image is also scaled to fit the dimensions
of dst.
src and dst cannot be the same.