Localized CAPTCHA

Question

What are effective CAPTCHA solutions that can have localized description, and CAPTCHA text itself is either language-neutral, or can be localized (for Polish language)? It is to be used to protect a kind of contact form.

reCAPTCHA (for example) allows i18n of the widget, but this still uses English source text that is then machine-translated. This makes it, I think, harder to solve for people who do not know English at all. I suspect it is even worse for the audio version of CAPTCHA.

Answer 1

It is not too difficult to roll your own basic CAPTCHA, or there are numerous tutorials and scripts out of the web.

I've used a simple one in PHP based on random letters/numbers, feel free to take and modify for your purpose:

// first generate random $string

$pa_captcha_salt = 'random stuff';
$hash = md5( $string.$pa_captcha_salt );
$filename = $_SERVER['DOCUMENT_ROOT'] . '/media/captcha/' . $hash . '.gif';

$font = 5; // font size
$width = ImageFontWidth($font) * strlen($string) + 4;
$height = ImageFontHeight($font) + 4;
$im = ImageCreateTrueColor($width, $height);

$textColor = ImageColorAllocate ($im, 99, 99, 99); // grey text
ImageString($im, $font, 2, 2, $string, $textColor);
ImageGif($im, $filename); // save file

Answer 2

Are you limited to scrambled text CAPTCHA's or will any Turing test work?

It would take more time to implement, but you could use one of the many other variations on challenge-response CAPTCHA in a localized environment.

My best recommendation would be to use a text-scrambling solution like the one offered by DisgruntledGoat with math questions - i.e. a slightly-wavy representation of "1 + 1 = ?" appears... but you have lots of other localization-ready options.