QUOTE(EL Wire @ Nov 13 2007, 05:01 AM)
My next question is how to use a jpg image as a layer and make it unaffected by the existing lighting.
You probably mean "camera rotoscope". In chorography, right-click on the camera, select "new" -> "rotoscope"
Are there some settings in the material properties to be made for that?
You can also decal a model and set it's "ambiance" to 100%. This way, it will look like it is casting light (although it is not) and will be unaffected by lights.
And what is the maximum jpg size accepted for use as a layer? I tried a large one and it came out blank.
If you render, your jpeg should show. The problem with large image files is that if they are larger than what the graphics card GPU can handle, they will display blank in the real-time preview.