一段实用的php验证码函数，php验证码

<?php
 
 function code(){
 
 $im = imagecreatetruecolor(100, 40);
 
 $black = imagecolorallocate($im, 0, 0, 0);
 
 $white = imagecolorallocate($im, 255, 255, 255);
 
 
 
 imagefill($im,0,0,$white);
 
 $strarr=array_merge(range(0,9),range(a,z),range(A,Z));
 
 shuffle($strarr);
 
 $str=join(array_slice($strarr,0,4));
 
 $mm=rand(0,40);
 
 $aaa=rand(0,0);
 
 $bbb=rand(0,255);
 
 $ccc=rand(0,255);
 
 $color1=imagecolorallocate($im,$aaa,$bbb,$ccc);
 
 imagestring($im,5,$mm,10,$str,$color1);
 
 for($i=0;$i<700;$i++){
 
   $aa=rand(0,255);
 
   $bb=rand(0,255);
 
   $cc=rand(0,255);
 
 $color=imagecolorallocate($im,$aa,$bb,$cc);
 
   $a=rand(0,100);
 
   $b=rand(0,40);
 
   imagesetpixel($im,$a,$b,$color);
 
 }
 
 for($t=0;$t<3;$t++){
 
   $a1=rand(0,255);
 
   $b1=rand(0,255);
 
   $c1=rand(0,255);
 
 $color2=imagecolorallocate($im,$a1,$b1,$c1);
 
   $a2=rand(0,100);
 
   $b2=rand(0,40);
 
   $a3=rand(0,100);
 
   $b3=rand(0,40);
 
   imageline($im,$a2,$b2,$b3,$b3,$color2);
 
 }
 
 
 
 header("content-type:image/png");
 
 imagepng($im);
 
 }
 
 code() ;
 
?>

function _code($_code_length = 4, $_width = 75, $_height = 25){
 for($i=0;$i<$_code_length;$i++){
  $_nmsg .= dechex(mt_rand(0,15));
 }
 $_SESSION["code"] = $_nmsg;

 $_img = imagecreatetruecolor($_width, $_height);

 $_white = imagecolorallocate($_img, 250, 250, 250);

 imagefill($_img, 0, 0, $_white);

 $_gray = imagecolorallocate($_img, 196, 196, 196);

 imagerectangle($_img, 0, 0, $_width-1, $_height-1, $_gray);

 for ($i=0; $i < 6; $i++) { 
  $_md_color = imagecolorallocate($_img, mt_rand(200,255), mt_rand(200,255), mt_rand(200,255));
  imageline($_img, mt_rand(0,$_width), mt_rand(0, $_height),mt_rand(0,$_width), mt_rand(0, $_height), $_md_color);
 }

 for ($i=0; $i < 50; $i++) { 
  $_md_color = imagecolorallocate($_img, mt_rand(200,255), mt_rand(200,255), mt_rand(200,255));
  imagestring($_img, 1, mt_rand(1,$_width-5), mt_rand(1, $_height-5), "*", $_md_color);
 }

 for ($i=0; $i < $_code_length ; $i++) { 
  $_md_color = imagecolorallocate($_img, mt_rand(0,102), mt_rand(0,102), mt_rand(0,102));
  imagestring($_img, 5, $i * $_width/$_code_length+ mt_rand(1, 10), mt_rand(1, $_height/2), $_SESSION["code"][$i], $_md_color);
 }

 header("Content-Type:image/png");

 imagepng($_img);

 imagedestroy($_img);
}

/*@ captcha()函数的功能：生成验证码
 * @ 可自定义参数：
 * @ $width 图片宽度，默认80
 * @ $high 高度，默认25
 * @ $num 验证码个数，默认4个
 * @ $line_num 随机画线条的个数，默认10
 * @ $snow_num 随机雪花的数量，默认50
 */
function captcha($width=80,$high=25,$num=4,$line_num=10,$snow_num=50){
 header('Content-Type:image/png');
 session_start();
 //生成随机数字＋字母
 for($a = 0;$a < $num;$a++){
  $code .= dechex(mt_rand(0, 15));//dechex — 十进制转换为十六进制
 }
 //把生成的验证码保存在SESSION超级全局数组中
 $_SESSION['captcha'] = $code;
 //创建画布
 $img = imagecreatetruecolor($width,$high);
 //填充背景色为白色
 $backcolor = imagecolorallocate($img, '255', '255', '255');
 imagefill($img, '0', '0', $backcolor);
 //添加黑色边框
 $bordercolor = imagecolorallocate($img, 0, 0, 0);
 imagerectangle($img, 0, 0, $width-1, $high-1, $bordercolor);
 //随机画线条
 for($i=0;$i<$line_num;$i++){
  imageline($img, mt_rand(0, $width*0.1), mt_rand(0, $high), mt_rand($width*0.9, $width), mt_rand(0, $high),
  imagecolorallocate($img, mt_rand(150, 255), mt_rand(150, 255), mt_rand(150, 255)));
 }
 //随机打雪花
 for ($i=0;$i<$snow_num;$i++){
  imagechar($img,1, mt_rand(0, $width), mt_rand(0, $high),'*',
  imagecolorallocate($img, mt_rand(200, 255), mt_rand(200, 255), mt_rand(200, 255)));
 }
 //画验证码
 for ($b = 0;$b < strlen($_SESSION['captcha']);$b++){
  imagechar($img,5, $b*$width/$num+mt_rand(5,10), mt_rand(2, $high/2),$_SESSION['captcha'][$b],
  imagecolorallocate($img, mt_rand(10, 150), mt_rand(10, 150), mt_rand(0, 100)));
 }
 ob_clean();//清空输出缓冲区
 imagepng($img);
 imagedestroy($img);
}