/modules/captcha/classes/libraries/captcha/driver/basic.php

<?php
/**
 * Captcha driver for "basic" style.
 *
 * @package		Modules
 * @subpackage	Captcha
 * @author		EightPHP Development Team
 * @copyright	(c) 2009-2010 EightPHP
 * @license		http://license.eightphp.com
 */
class Captcha_Driver_Basic_Core extends Captcha_Driver {

	/**
	 * Generates a new Captcha challenge.
	 *
	 * @return  string  the challenge answer
	 */
	public function generate_challenge() {
		// Complexity setting is used as character count
		return str::random('distinct', max(1, Captcha::$config['complexity']));
	}

	/**
	 * Outputs the Captcha image.
	 *
	 * @param   boolean  html output
	 * @return  mixed
	 */
	public function render($html) {
		// Creates $this->image
		$this->image_create(Captcha::$config['background']);

		// Add a random gradient
		if(empty(Captcha::$config['background'])) {
			$color1 = imagecolorallocate($this->image, mt_rand(200, 255), mt_rand(200, 255), mt_rand(150, 255));
			$color2 = imagecolorallocate($this->image, mt_rand(200, 255), mt_rand(200, 255), mt_rand(150, 255));
			$this->image_gradient($color1, $color2);
		}

		// Add a few random lines
		for($i = 0, $count = mt_rand(5, Captcha::$config['complexity'] * 4); $i < $count; $i++) {
			$color = imagecolorallocatealpha($this->image, mt_rand(0, 255), mt_rand(0, 255), mt_rand(100, 255), mt_rand(50, 120));
			imageline($this->image, mt_rand(0, Captcha::$config['width']), 0, mt_rand(0, Captcha::$config['width']), Captcha::$config['height'], $color);
		}

		// Calculate character font-size and spacing
		$default_size = min(Captcha::$config['width'], Captcha::$config['height'] * 2) / (strlen($this->response) + 1);
		$spacing = (int) (Captcha::$config['width'] * 0.9 / strlen($this->response));

		// Draw each Captcha character with varying attributes
		for($i = 0, $strlen = strlen($this->response); $i < $strlen; $i++) {
			// Use different fonts if available
			$font = Captcha::$config['fontpath'].Captcha::$config['fonts'][array_rand(Captcha::$config['fonts'])];

			// Allocate random color, size and rotation attributes to text
			$color = imagecolorallocate($this->image, mt_rand(0, 150), mt_rand(0, 150), mt_rand(0, 150));
			$angle = mt_rand(-40, 20);

			// Scale the character size on image height
			$size = $default_size / 10 * mt_rand(8, 12);
			$box = imageftbbox($size, $angle, $font, $this->response[$i]);

			// Calculate character starting coordinates
			$x = $spacing / 4 + $i * $spacing;
			$y = Captcha::$config['height'] / 2 + ($box[2] - $box[5]) / 4;

			// Write text character to image
			imagefttext($this->image, $size, $angle, $x, $y, $color, $font, $this->response[$i]);
		}

		// Output
		return $this->image_render($html);
	}

} // End Captcha Basic Driver Class