[ydant]

My source (chalkboard) image wasn't great (dark, low contrast), but I got better results from the service by doing an "invert" before sending it on.

[kyleburton]

Awesome! Would you be willing to share a chalkboard pic? I don't have access to one...thanks for the invert tip!

[ydant]

You know this already, but I sent them to your email as in your HN profile.

I have no idea how important blackboard is - probably less so for the business world, but plenty of students use/encounter them.

If it's easy to work out a algorithm that cleans up the blackboard but harder to work out detecting the blackboard, your idea of two email addresses (doodle/wb@, and blackboard/bb@) would probably be a good solution.