php结合GD库生成验证码的例子（w3c推荐）

使用PHP，结合session和GD库扩展开发的一个生成验证码的例子（w3c推荐）。可以很方便的用于项目中。而且样式美观大方。

/** 

演示地址：http://www.pooy.net/captcha/ 

原文出处：http://www.pooy.net/php-captcha.html 

下载地址：http://pan.baidu.com/share/link?shareid=517762&uk=3240790330 

**/

//首先开启session 

session_start(); 

//定义前台显示验证码长&宽 

$image_width = 120; 

$image_height = 40; 

$characters_on_image = 6; 

$font = './monofont.ttf'; 

//The characters that can be used in the CAPTCHA code. 

//avoid confusing characters (l 1 and i for example) 

$possible_letters = '23456789bcdfghjkmnpqrstvwxyz'; 

$random_dots = 10; 

$random_lines = 30; 

$captcha_text_color="0x142864"; 

$captcha_noice_color = "0x142864"; 

//定义要生成验证码的字符串 

$code = ''; 

$i = 0; 

while ($i < $characters_on_image) { 

$code .= substr($possible_letters, mt_rand(0, strlen($possible_letters)-1), 1); 

$i++; 

} 

$font_size = $image_height * 0.75; 

$image = @imagecreate($image_width, $image_height); 

/* setting the background, text and noise colours here */

$background_color = imagecolorallocate($image, 255, 255, 255); 

$arr_text_color = hexrgb($captcha_text_color); 

$text_color = imagecolorallocate($image, $arr_text_color['red'], 

        $arr_text_color['green'], $arr_text_color['blue']); 

$arr_noice_color = hexrgb($captcha_noice_color); 

$image_noise_color = imagecolorallocate($image, $arr_noice_color['red'], 

        $arr_noice_color['green'], $arr_noice_color['blue']); 

/* generating the dots randomly in background */

for( $i=0; $i<$random_dots; $i++ ) { 

imagefilledellipse($image, mt_rand(0,$image_width), 

 mt_rand(0,$image_height), 2, 3, $image_noise_color); 

} 

/* generating lines randomly in background of image */

for( $i=0; $i<$random_lines; $i++ ) { 

imageline($image, mt_rand(0,$image_width), mt_rand(0,$image_height), 

 mt_rand(0,$image_width), mt_rand(0,$image_height), $image_noise_color); 

} 

/* create a text box and add 6 letters code in it */

$textbox = imagettfbbox($font_size, 0, $font, $code); 

$x = ($image_width - $textbox[4])/2; 

$y = ($image_height - $textbox[5])/2; 

imagettftext($image, $font_size, 0, $x, $y, $text_color, $font , $code); 

/* Show captcha image in the page html page */

header('Content-Type: image/jpeg');// defining the image type to be shown in browser widow 

imagejpeg($image);//showing the image 

imagedestroy($image);//destroying the image instance 

//设置session，做验证 

$_SESSION['6_letters_code'] = $code; 

function hexrgb ($hexstr) 

{ 

  $int = hexdec($hexstr); 

  return array("red" => 0xFF & ($int >> 0x10), 

               "green" => 0xFF & ($int >> 0x8), 

               "blue" => 0xFF & $int); 

} 

/** 

演示地址：http://www.pooy.net/captcha/ 

原文出处：http://www.pooy.net/php-captcha.html 

下载地址：http://pan.baidu.com/share/link?shareid=517762&uk=3240790330 

**/