I have a scene where I have a car mirror and I want it to reflect a different image than the world settings image. I can think of a couple of ways to do it but I was hoping one of you guys out there maybe knew how to do it the right way…;). Do you have to use multiple layers?
Much appreciated… 
In F6, Texture tab, under Texture Type, use an Environment Map (EnvMap). Take the mirror to an empty layer. Map the Image you want reflected to the World and render. Save the EnvMap Image. Move the mirror back to its original layer. Now when you’re ready for the final render you can load the saved EnvMap Image and as long as you don’t “Free Data” the saved image is what will render as reflection.
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Here’s a simple composite node map for replacing an object with another image, sort of like the “portals” you see in some 3d games. I’m just blending in a static image I had laying around, but I think you could also use, say, a RenderLayers input attached to a camera in a different scene.
The cube-thing’s on its own layer with nothing else, and the lower renderlayer is set to ignore every layer but that one; the upper one is set to use every layer but that one.
The alpha looks a bit strange near the top of the composite preview, but it showed up fine in the actual render, against sky.
