You need to control the render order using the ‘automatic 0’ argument in your gl objects and send them bangs in the order you wish to render them. Check the forum for some examples of how to do this. This thread (amongst many others) has some examples of how to do it : http://www.cycling74.com/forums/index.php?t=msg&th=18925
To put a picture on top, you can use a jit.gl.videoplane
make sure you set all opengl object to @automatic 0, then draw them
individually in the order than you want, draw your picture at last. You
might want to search the list for "orho 2" if you want the picture at a
fixed position while changing camera positions and lens angles.