Lets go! I believe it is this what you want.
To place an imagem in front of you scene, you have to use the sequence editor. Quick explanation ahead.
1 Go to the sequence editor window
2 “Shift+A>Images” locate the image you are going to use in the foreground.
Note that this image must have an alpha data. My sugestion is: make a selection around the object you want to show and save the image as .tga with RLE compression on.
3 “Shift+A>Scene” and select the scene you want to show in the background.
4 Select the scene strip, them select the image strip and “Shift+A>Alpha Over”. Place the Alpha Over strip over the other two strips.
Important: You must select the strips in the correct order. If you select in a different order you will get an undesirable effect (in this case)
5 Place the background image as an world texture
Note: take a look in the map to options
6 Select the option “do sequence” bellow the Anim buttom in F10 menu
Voilá! you now have and image with 3 layers: The girl (image w/ alpha), the monkey (3d object in the scene) and the volcano (world texture)
All of them can be animated. The girl: use a image sequence and select the hole sequence in the “shift+A” menu. The monkey: well, there are several ways to do it. The volcano: animated texture (image sequence or movie file)
Hope it helps!