I need to apply a captcha to one of my clients forms.

Can anyone recommend a good one?  Here's what I'm looking for...

Must have the following...
- Free
- Good looking & Subtle (not too many gaudy colours & not too bulky)
- Either PHP/JavaScript (not ASP)
- Option to refresh and get another image if current one is bad
- Option to exclude certain letters and numbers (like 0 & O)

Would be nice if it had the following...
- Audio for those with disabilities
- Aesthetics customisable via css

no need for an image based captcha - use maths and human sense

pick two random numbers between 1 and 10 and a random operator (+,-,*,/) and ask the user to put the answer to the calculation in the form field.

To perform the validation you must know what the original question was and then check the answer with that submitted

The easiest/crudest way i can think of is to use md5

an example in PHP

as part of the form

<?php





$var1 = rand(1,10);

$var2 = rand(1,10);

$op = rand(0,2);



$ops = array('+','-','*');          // I removed '/' to avoid things like 3/7 - ensuring only integers come back!



$expr = $var1." ".$ops[$op]." ".$var2;



eval('$result = '.$expr.';');



?>



echo $expr." = <input type='text' name='auth' />";

echo "<input type='hidden' name='authc' value='".(md5($result))." ?>' />";



?>

Once submitted, check like this

<?php



if($_POST['authc'] == md5($_POST['auth'])) {

        //ok

} else {

        //not ok

}



?>

This is also a pretty cool one

http://recaptcha.net/

you get two images, both have been scanned in from a book and parsed through OCR software. The OCR recognised one, but not the other.

You get the user to enter both words. If the word that is known is matched correctly then thats ok.

The other word the user enters is taken to be the deciphered word, correctly spelled and is stored in their database - all in all you are helping to convert books into an electronic format....and you get a captcha!

Here are some I have bookmarked.

Very versatile but takes a little bit to set up.
http://www.dagondesign.com/articles/sec … er-script/

http://www.freecontactform.com/

This has both image and audio
http://www.boutell.com/newfaq/creating/captcha.html

I use one like Northie suggested on my tutorial site.
http://validwebdesigns.com/contactvwd.php

Hey guys.  Fantastic!  Thanks so much for all the suggestions!
I'm going to look through all of those now and see what fits best.

Ok, so I'm really liking the maths one (freecontactform) which is pretty much what Northie was describing only 99% of the thinking work is done for me.  There was just one thing I didn't like, but it was quick to change - I just changed it so that the name is added to the from field instead of just an email address and that's pretty much perfect, so I even added it to my own site.

Thanks again!