Developing Image Authentication Control

I just start developing another ASP.NET Control that allows users to authenticate via text rendered on a image.

This is my Goal:

• Easy to read

• Eliminating ambiguous letter such as o,O,and 0.
• Simple Alphabets and Numbers

• Hard to crack

• Changing color
• Drawing random lines
• Drawing random dots
• Rotate / Transform the characters

• Quick to generate

• Matrix Operation using Unsafe code(?)

OK, this is very regular way to implement this kind of control, so I was thinking of the future extention:

• Like KittenAuth ?
• Voice support
• WebService (SOAP/WSDL)

KittenAuth is interesting approach to increase the security level. It shows a buch of pictures and a user selects which one looks like purr animal. In version 2.0, it is mixing the kind of animals too.