我们先来检查一下自己的php是不是打开了gd库。

复制代码 代码如下:

if(extension_loaded('gd')) {

echo '你可以使用gd
';

foreach(gd_info() as $cate=>$value)

echo "$cate: $value
";

}else

echo '你没有安装gd扩展';

?>

如果有返回信息就正确可以常用使用了

例1

复制代码 代码如下:

/**

* vCode(m,n,x,y) m个数字  显示大小为n   边宽x   边高y

* 自己改写记录session $code

*/

session_start();

vCode(4, 15); //4个数字，显示大小为15

function vCode($num = 4, $size = 20, $width = 0, $height = 0) {

!$width && $width = $num * $size * 4 / 5 + 5;

!$height && $height = $size + 10;

// 去掉了 0 1 O l 等

$str = "23456789abcdefghijkmnpqrstuvwxyzABCDEFGHIJKLMNPQRSTUVW";

$code = '';

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

$code .= $str[mt_rand(0, strlen($str)-1)];

}

// 画图像

$im = imagecreatetruecolor($width, $height);

// 定义要用到的颜色

$back_color = imagecolorallocate($im, 235, 236, 237);

$boer_color = imagecolorallocate($im, 118, 151, 199);

$text_color = imagecolorallocate($im, mt_rand(0, 200), mt_rand(0, 120), mt_rand(0, 120));

// 画背景

imagefilledrectangle($im, 0, 0, $width, $height, $back_color);

// 画边框

imagerectangle($im, 0, 0, $width-1, $height-1, $boer_color);

// 画干扰线

for($i = 0;$i < 5;$i++) {

$font_color = imagecolorallocate($im, mt_rand(0, 255), mt_rand(0, 255), mt_rand(0, 255));

imagearc($im, mt_rand(- $width, $width), mt_rand(- $height, $height), mt_rand(30, $width * 2), mt_rand(20, $height * 2), mt_rand(0, 360), mt_rand(0, 360), $font_color);

}

// 画干扰点

for($i = 0;$i < 50;$i++) {

$font_color = imagecolorallocate($im, mt_rand(0, 255), mt_rand(0, 255), mt_rand(0, 255));

imagesetpixel($im, mt_rand(0, $width), mt_rand(0, $height), $font_color);

}

// 画验证码

@imagefttext($im, $size , 0, 5, $size + 3, $text_color, 'c:\WINDOWS\Fonts\simsun.ttc', $code);

$_SESSION["VerifyCode"]=$code;

header("Cache-Control: max-age=1, s-maxage=1, no-cache, must-revalidate");

header("Content-type: image/png;charset=gb2312");

imagepng($im);

imagedestroy($im);

}

?>

例2

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

复制代码 代码如下:

//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

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

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);

}

个人推荐推荐第二个生成验证码程序代码，各位同学可尝试参考对比哦，最后一个是W3C标准生成的也是利用了php gd库。