resizing reference after giving specific dimensions I'm trying to model a room from reference images. I know it's exact sizes,
and can change it to that in the properties. The reference picture will not change with that of course, how do i resize and place the reference in the correct way?
How about 


create a plane
assign it a texture with your ref image (some UV mapping/unwrapping required to match the entire image)
Size it and use it in the background in Ortho view 
repeat for front/side views with different pictures!