Hi John,
You'll need to find a bitmap editor application that exposes a VBA
object model.
Recent versions of Corel Photo-Paint do this, though I've never tried to
use it. I have read that the VBA object model is not complete and that
it's often necessary to use Corel Script to program the operations you
need and then call the Corel Script procedure from VBA.
http://www.oberonplace.com/ looks like a good place to start
researching.
This
http://partners.adobe.com/public/developer/photoshop/sdk/index_scripting.html
suggests that PhotoShop too can be controlled from VB. I haven't
investigated whether this means classic VB (and therefore VBA) or
VB.Net.