/**

*产生验证码图片

*/

public function actionVerfiycode() {

Header ( "Content-type: image/gif" );

$border = 0; //是否要边框 1要:0不要

$how = 4; //验证码位数

$w = $how * 15; //图片宽度

$h = 20; //图片高度

$fontsize = 5; //字体大小

$alpha = "abcdefghijkmnopqrstuvwxyz"; //验证码内容1:字母

$number = "0123456789"; //验证码内容2:数字

$randcode = ""; //验证码字符串初始化

srand ( ( double ) microtime () * 1000000 ); //初始化随机数种子

$im = ImageCreate ( $w, $h ); //创建验证图片

$bgcolor = ImageColorAllocate ( $im, 255, 255, 255 ); //设置背景颜色

ImageFill ( $im, 0, 0, $bgcolor ); //填充背景色

if ($border) {

$black = ImageColorAllocate ( $im, 0, 0, 0 ); //设置边框颜色

ImageRectangle ( $im, 0, 0, $w - 1, $h - 1, $black ); //绘制边框

}

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

$alpha_or_number = mt_rand ( 0, 1 ); //字母还是数字

$str = $alpha_or_number ? $alpha : $number;

$which = mt_rand ( 0, strlen ( $str ) - 1 ); //取哪个字符

$code = substr ( $str, $which, 1 ); //取字符

$j = ! $i ? 4 : $j + 15; //绘字符位置

$color3 = ImageColorAllocate ( $im, mt_rand ( 0, 100 ), mt_rand ( 0, 100 ), mt_rand ( 0, 100 ) ); //字符随即颜色

ImageChar ( $im, $fontsize, $j, 3, $code, $color3 ); //绘字符

$randcode .= $code; //逐位加入验证码字符串

}

for($i = 0; $i < 5; $i ++) //绘背景干扰线

{

$color1 = ImageColorAllocate ( $im, mt_rand ( 0, 255 ), mt_rand ( 0, 255 ), mt_rand ( 0, 255 ) ); //干扰线颜色

ImageArc ( $im, mt_rand ( - 5, $w ), mt_rand ( - 5, $h ), mt_rand ( 20, 300 ), mt_rand ( 20, 200 ), 55, 44, $color1 ); //干扰线

}

for($i = 0; $i < $how * 40; $i ++) //绘背景干扰点

{

$color2 = ImageColorAllocate ( $im, mt_rand ( 0, 255 ), mt_rand ( 0, 255 ), mt_rand ( 0, 255 ) ); //干扰点颜色

ImageSetPixel ( $im, mt_rand ( 0, $w ), mt_rand ( 0, $h ), $color2 ); //干扰点

}

$session=new CHttpSession;

$session->open();

Yii::app()->session->add('randcode',$randcode);

/*绘图结束*/

Imagegif ( $im );

ImageDestroy ( $im );

/*绘图结束*/

}

引自：

http://www.admin5.com/article/20080314/75984.shtml