The Camera Map modifier (world-space version) lets you blend an object into the background throughout the course of an animation.
The Camera Map world-space modifier is similar to the Camera Map object-space modifier, in that it applies UVW mapping coordinates to the object based on a specified camera. As a result, if you assign the same map as a Screen environment to the background as you apply to the object, the object is invisible in the rendered scene.
Interface

Current Camera Object group
- Label
-
Names the current camera used for mapping. If there is no current camera, reads "None."
- Pick Camera
-
Click this button, and then select the camera you want used for mapping.
Channel group
- Map Channel
-
Specifies use of a map channel. Map channels are specified in the Material Editor.
- Vertex Color Channel
-
Specifies use of the Vertex Color Channel (see UVW Map Modifier).