I was also thinking to add similar feature in my app Lekh Diagram (http://www.avabodh.com/lekh http://www.avabodh.com/lekh). I have not spent much time on this

I was also thinking to add similar feature in my app Lekh Diagram (http://www.avabodh.com/lekh http://www.avabodh.com/lekh). I have not spent much time on this yet but, IMO the biggest challenge in doing sketch recognition is to resolve ambiguity on interpreting recognized shape/strokes . A hand drawn shape can be interpreted differently by different people and can be interpreted differently in different context. A computer program interpreting exactly what user has intention, is a challenging task. But I believe that a system can be build which will probably work 90% of time correctly. Wishing good luck to these guys!!