I've also been playing with using my photos as backgrounds again - it's like Baggins Bill says - it's getting the shadows lined up and of the same length and "shade" that the key to making this work.   

My lastest stab is this one - straight Vue render - using IBL lighting - the only post work is using Optik Verves freebie plugin - Virtual Photographer [natural portrait setting] to add some grain and flatten the colours.  

Pinky - you left the lens cap of your mind on again.