The Camera Map world space modifier is similar to the Camera Map 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.
The main difference between the WSM version of Camera Map and the OSM version is that, when you move the camera or the object using the OSM version, the object becomes visible, because the UVW coordinates are fixed to the object’s local coordinates. When you move the camera or object using the WSM version, the object remains invisible because world coordinates are used instead.
The WSM Camera Map consists of a single Pick Camera button. Click the button, and then click the camera you want used.
Note: You can get a very similar effect to WSM Camera Map by applying a diffuse map to an object using environment mapping set to be the same method as the map used for the background. In that case, however, the object will remain invisible no matter which camera renders the scene. The WSM Camera Map, however, is set to a specific camera. Thus, you can manipulate the effect by alternating between two cameras that begin by sharing the same location. As you move the non-specified camera, the object becomes visible. If you switch back to the other camera, the object again is invisible.