For developing a web based scan solution, I would love to test it on Windows or Mac without actually hooking up a scanner to my box. So is there a program/tool that emulates or gives me a virtual twain source with some default image data?
The Twain sample driver that comes along with the twain sample application up on source forge should have what you're looking for.
http://sourceforge.net/projects/twain-samples/files/TWAIN%202%20Sample%20Application/