Basically you need to render the UV pass (enable Render Layers>>Passes>>UV) to use it in compositor with the MapUV node.
For better results, you’ll have to render also other passes (glossy, shadows, objectIndex etc), and play with them in compositor.
Render first time normally, then change photo image and render ONLY that image with alpha background. Might be faster to render photo image with Blender render. Finally mix 2 videos.