From the menu, choose 'Tools', and from that menu choose 'Open a Reference Image'
That will allow you to pin a reference photo to the canvas. You can more the pinned image to where you want by clicking in the middle and dragging it around. You can resize it by dragging the corners, and rotate it by dragging the edges. You can have as many references pinned to the canvas as you like.
Using the eye-dropper tool, you can also sample colours from the reference images.
AndyRage's mantra for graphics engine code:
"Sure - how hard can it be?"