Free PHP CAPTCHA Scripts
PHP Scripts to Generate an Image with Letters / Numbers
Free PHP CAPTCHA Scripts
These free CAPTCHA PHP scripts allow you to add a facility to your web forms to weed out the spam bots (automated programs that submit spam into your email contact forms and other such web forms) from the humans. They typically generate an image with some characters that your visitors have to type before they can successfully submit a form. Some of them also automatically generate an audio file with those characters read aloud for visually impaired visitors.
In general, it is not a trivial operation to modify your scripts to support CAPTCHA, since it usually requires some knowledge of both HTML and PHP. You should also know that CAPTCHA solutions can present accessibility problems to your visitors. For example, visually impaired people may not be able to read your CAPTCHAs, and are thus unable to use your forms. Even if your CAPTCHA has an audio file attached, it will only help those who are not deaf as well. People who are both blind and deaf, who depend on Braille (touch) displays to read your site will neither be able to view your CAPTCHA image nor hear your audio equivalent. In addition, some CAPTCHA scripts generate images are so difficult to read, that even people with normal eyesight have difficulty deciphering what it says. (I'm sure you've encountered such images before too, and have had to reload the page numerous times before you got a sequence of letters and numbers you could enter.)
For the curious, CAPTCHA stands for "Completely Automated Public Turing test to tell Computers and Humans Apart". The acronym is a trademark of Carnegie Mellon University.
If all you want is to insert a CAPTCHA test into your feedback form, and don't really want to muck around with writing your own PHP code, you may want to consider using thesitewizard.com's Free Feedback Form Wizard which has a facility to easily add a CAPTCHA test without your needing any programming knowledge. It's free and has no ads or anything like that.
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Free CAPTCHA PHP Scripts
- PHP Captcha
This CAPTCHA displays a JPEG image containing a 6-character random string of letters and numbers for your visitors. It requires GD to be installed on your server.
- Securimage: Free PHP CAPTCHA Script
Securimage generates a complex image and CAPTCHA code for your forms and form-processing scripts. Including this code in your form to mail script and web form allows your script to check if the form submitter is a human or just a spam bot. It requires GD to be installed on your server. The script allows you to customize the length of the CAPTCHA code, choose the character set, use custom GD fonts if TrueType fonts are not available, add background images, create arcs (lines) through text, create multi-coloured, angled and transparent text, generate an audible CAPTCHA file in WAV format for the blind, provide a word list that the script can use, etc. It also has a WordPress plugin, so you can easily add it to your blog if you use that particular blogging script.
- Free CAPTCHA Service
This free CAPTCHA service provides code for you to integrate into your script and form, be it a feedback or contact form or some other type. You will have to register with them for the service to get a key to include into the PHP code.
- FreeCap: PHP CAPTCHA Script
(Update: this service appears to have closed.) Like the other free CAPTCHA scripts on this page, this script generates a CAPTCHA code for your email forms and other web forms. Besides generating characters for your visitor to enter into the form, it also randomly creates a background image consisting either of grids, squiggles or image blocks probably to confuse robots with optical character reading facilities. The script supports multiple fonts and colours, uses a customizable dictionary, and so on. The site also has plugins for a variety of CMS and blogging software.
- Asirra
(Update: Assira is permanently closed as of October 2014. For the record, the site was originally at
http://research.microsoft.com/en-us/um/redmond/projects/asirra/. At the time I added this note, the documentation is still there, but you can no longer use the service.) Asirra, from Microsoft Research, provides your visitors with a set of pictures of cats and dogs. To prove that they are human, your visitors will have to click the pictures that they think are cats. The service relies on JavaScript to be available on your visitor's browser, which is needed to display the pictures and do some preliminary checking. You will also have to modify your feedback form's PHP code to send the code entered by your visitor to the Asirra servers for checking, and then parse the XML data returned to find out if there was a match.
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