I like to sculpt from reference photos and drawings, however up till now these had to be strictly Orthographic - In line with the axes and with no perspective distortion.
I've been trying out a new photo-fit backdrop that allows for any angle backdrops, with perspective distortion. You just tag reference points in 3D and on your image and it lines them up. It works well with multiple angles of the same object.
Below I took a bunch of photos of Jason Statham from Google - all from varied angles and perspectives, and unified them with the new backdrop fitter. Having a group of reference images ready lined up is very handy. (Notice in the bottom left a list of my 8 backdrops)
You could use the same idea to fit a 3D object into an existing 2D picture by matching the angle and perspective using the same tools.