Personal observation, bitmaps are drawing surfaces but can't be resized. They can be written to images. With images you typically have a static "picture" but can manipulate them using the sprite properties. You can't draw to the image directly. No Dark GDK commands allow you to draw boxes,circles or dots.
That said, you can get past some of these limitations on images if you're willing to dig down into the Direct X surfaces. I've written a rudimentary Image class that allows me to draw circles and boxes, filled and unfilled, and dots on the image surface.
Lilith, Night Butterfly
I'm not a programmer but I play one in the office