Auto submissions protection for HTML forms

Hello there,

I've asked this question already in Spring's forum, but I'll need this for my old Struts application, so I am asking it here too.

I need to develop Web application and I do need to have this nice feature for bunch of HTML forms which prevents auto submissions.

I mean I need this like question "type number which you see on the image", and it will not allow you to submit with properly typed image.

So the question is -- is there are any specific separate open source framework for this feauture?

Any advice will be helpful!!! Thanks!

The name for this type of control is "captcha". Try this link for one such project.