May I know the best way to test "Robot or Human" in .Net (In Web with C#.Net)

Hi Every One,

Happy new year. I have one question to ask this big Stack Over Flow community. Could any one please suggest be the best way to perform "Robot" or "Human" test in .Net applications. Above Image, I copied from gmail while creating account(thanks to google). I'm planning to perform similar validation before creating the account in my .Net web Application. So, please suggest the best approach.

Thanks i开发者_StackOverflown advance.

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Recaptcha is one of the better/best services I am aware of that makes this really easy for you as a developer:

http://www.google.com/recaptcha