Simple php server based captcha using GD
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PHP Captcha

Since Google and others are abusing Captchas to be tracking utilities, it was time to write a server based Captcha. Since the data are processed on your webserver only, this Captcha is GDPR safe. PHP Captcha does not forward any data away from your server. You do not need to mention it in your privacy policy. But of course I would like it very much, if you could add a reference to this project.

License

PHP Captcha is available under the terms of GPLv3. See License for more information.

Requirements

PHP Captcha is using GD to generate images. PHP5 and PHP7 are supported.

How to install

  1. Download the latest release here: https://github.com/pstimpel/phpcaptcha/releases
  2. Unpack the content of the zip into a folder on your webserver, let's say to modules in your webroot
  3. Use your webbrowser and browse to <Your webserver>/modules/phpcaptcha-<version>/index.php
  4. If 3. works fine, you could configure PHP Captcha by editing <Your webroot>/modules/phpcaptcha-<version>/config.php

Configuration options

_Do not attempt a change of your configuration until you finished step 3 of the installation with success! _

stringLength: How many characters to use for the captcha, default is 6

charsToUse Which characters to choose from, default is abcdefghkmnprstuvwxyz23456789, it might be a good idea to skip characters like I and 1 for avoiding confusion

strictLowerCase: Limit captcha to lower case, default is true, if there are no upper case characters in your charsToUse, this option is useless

bgcolor.r: Red value of background color, default is 0, valid from 0 to 255

bgcolor.g: Green value of background color, default is 0, valid from 0 to 255

bgcolor.b: Blue value of background color, default is 0, valid from 0 to 255

textcolor.r: Red value of text color, default is 255, valid from 0 to 255

textcolor.g: Green value of text color, default is 255, valid from 0 to 255

textcolor.b: Blue value of text color, default is 255, valid from 0 to 255

font: Name of TTF font to use, default is 'Lato-Regular.ttf', but you can use any TTF font you like.

Font Lato is GPL, OFL and Public Domain by Łukasz Dziedzic, can be found at https://www.1001freefonts.com/lato.font

sessionName: The name of the session var PHP Captcha is using to store the text from the captcha, default is phpcaptcha, which is accessible in $_SESSION['phpcaptcha']

size.width: The width of the generated image, default is 200

size.height: The height of the generated image, default is 50

fontsize: The font size to be used, default is 25

numberOfLines: The number of lines to draw across the image for creating some small confusion to OCR, default is 6

thicknessOfLines: The thickness per line, default is 2

linecolor.r: Red value of line color, default is 128, valid from 0 to 255

linecolor.g: Green value of line color, default is 128, valid from 0 to 255

linecolor.b: Blue value of line color, default is 128, valid from 0 to 255

How to use it?

There is a Demo available, if you unzipped the package at your webserver. Just navigate to the demo subfolder using your webbrowser. If GD is missing, PHP Captcha will detect it and throw an error. If you misconfigured PHP Captcha, it will try to run on defaults, or throw an error depending on the type of your failure.

If it was installed and configured well, just reference <Your webserver>/modules/phpcaptcha/index.php as image in your html form.

Example:

<img src="https://yourserver/modules/phpcaptcha-<version>/index.php" />

You will have to add a textfield to your form as well, so the user can type in what he/she/it sees on the captcha image. Let's do it like this:

<input type="text" name="captchatext" value="">

Now, make a check where you evaluate the form data. A simple

if($_POST['captchatext'] == $_SESSION['phpcaptcha']) {
    //Captcha solution OK
} else {
    //Captcha solution wrong
}

will do. Of course you should run checks like isset() on both variables before...

However, you are ready to go, congrats!