Extract from the Member Agreement:
b. With respect to Content you submit to the Reference Image Library, you grant to all other users of the web site a royalty-free, perpetual, non-exclusive, world-wide, irrevocable right and license to use your uploaded images as reference images in the creation of new artwork in a different medium (such as painting, sculpture, and so on), and to sell the artwork they create pursuant to this license to use the image. You do not grant other users the right to digitally alter the image or to otherwise use or sell the image in its unaltered state. You retain the copyright to the original image.
So you may only use them as references, not as a photograph.