u should set the ratio to 3:2 for 4R size.
dat means the size must be something like 300:200 pixel or 360:240..
easier way is to use photoshop and select the marquee toolon the left,usually the top left option,then right on top there is an option called constrained ratio,select that one and set it to 3:2 then u can begin cropping the photo..
did i confuse u ?