Its a good idea to get your images centered in a image editing software such as Photoshop when creating reference images.
Centering the Image
I want my image to line up with the center of my grid in Max. This is where Photoshop comes in. Take the image in, and create a guide in the middle and then shift the bunny over until he is as close to being divided down the middle as possible.
Virtual Studio blog from Trance Lion on Vimeo.