Well, although ArtRage isn't really intended as a digital image editor, you can do a bit of image compositing by using tracing paper, and converting it to paint.
Create a new painting. Load one of the images you want to composite as a tracing image. Use the tracing image editing tools to size and position the image (choose 'manual scale' from the scale options). Hit 'Done' when the image is in the correct place. Then select 'Convert tracing image to paint on this layer' from the menu.
That will drop the tracing paper into the layer as if it were painted there. Repeat for your other images.
If your images have transparency (alpha) in places, that will let you have areas other than just rectangular pasted in.
And dont forget to clear the last tracing image so you can clearly see your resultant composition.
AndyRage's mantra for graphics engine code:
"Sure - how hard can it be?"