If your reference image is cropped to precise size, and if you know the dimensions of height and width, draw a box to those dimensions to suit the view you have, then place the image using the corner snaps and everything should then be in place ... there is a thread here recently about scaling and positioning hopefully Michael will remember it and throw you a pointer to it.

Martin Spencer-Ford

Found it .... http://moi3d.com/forum/index.php?webtag=MOI&msg=1982.9 (see if that works for you)