Captcha installed but verification not working

Just installed the Captcha mod. The installation seems to be ok and the images shows asking for verification...but the verification doesn't work. In the contact us I can fill all the fields and even leaving the verficiation field empty the message is sent not caring at all about the verification...any suggestion to solve the problem?

I am using ZC v1.3.8a.

Thanks!

Problem solved.

I did the stupid mistake of remaning the old file like:

filename_old.php

in the same folder with the new one:

filename.php

What happened: that the old file was executed as well as the new one and the old one, of course, was without validation for the captcha so the message was sent using the code in the old file. If you want to keep a copy of the old file, just in case something doesnt' work and you want to go back to the previous version, just rename the file in something like filename.old instead than filename_old.php. Or, much better, perform a backup of the whole code and forget about it.

To discover if you are affected about this kind of problem, just leave the form blank and hit the "Send" button. If the warning messages coming out are duplicated than you probably have something similar.