Well, there are no personal feelings here: if the image is a photo,
then Y should point up: I believe that when I see a map or a
landscape, I measure things higer in higher coordinates.
If the image is a drawing, then all draftsmen would agree to have Y
point up.
The ONLY case in which I can see a slight advantage to have Y point
down is text, and that should be editable text, not pixels. A
PostScript original image certainly has Y pointing up. This is also
the only reason that was taken for pointing Y down on bitmapped
displays: it was just an extension of the line-count on character
grid terminals.
Just think of placing the sensitive rectangles using real tools on a
screen: When I place a rectangle in any serious drawing program I
know of (I do not include MacPaint of course!), the position of the
mouse is given with Y pointing up.
This is what we have to think of, not what has already been done.
Robert.