PHP生成验证码的函数，实用靠谱。先上下生成的验证码的效果图（这里生成的是全数字的验证码的示例效果）：
PHP;">
PHP
session_start();
//session_register('CheckCode');
//PHP4.2以上版本不需要用session_register()注册SESSION变量
$type='gif';
$width= 45;
$height= 20;
header("Content-type: image/".$type);
srand((double)microtime()*1000000);
if(isset($_GET['action'])){
$randval=randStr(4,$_GET['action']);
}else{
$randval=randStr(4,'');
}
if($type!='gif'&&function_exists('imagecreatetruecolor')){
$im=@imagecreatetruecolor($width,$height);
}else{
$im=@imagecreate($width,$height);
}
$r=Array(225,211,255,223);
$g=Array(225,236,237,215);
$b=Array(225,166,125);
$key=rand(0,3);
$backColor=ImageColorAllocate($im,$r[$key],$g[$key],$b[$key]);//背景色（随机）
$borderColor=ImageColorAllocate($im,127,157,185);//边框色
$pointColor=ImageColorAllocate($im,170,255);//点颜色
@imagefilledrectangle($im,$width - 1,$height - 1,$backColor);//背景位置
@imagerectangle($im,$width-1,$height-1,$borderColor); //边框位置
$stringColor=ImageColorAllocate($im,51,153);
for($i=0;$i<=100;$i++){
$pointX=rand(2,$width-2);
$pointY=rand(2,$height-2);
@imagesetpixel($im,$pointX,$pointY,$pointColor);
}
@imagestring($im,5,1,$randval,$stringColor);
$ImageFun='Image'.$type;
$ImageFun($im);
@imagedestroy($im);
$_SESSION['CheckCode']=$randval;
function randStr($len=6,$format='ALL'){
switch($format){
case 'ALL'://生成包含数字和字母的验证码
$chars='ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789'; break;
case 'CHAR'://仅生成包含字母的验证码
$chars='ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz'; break;
case 'NUMBER'://仅生成包含数字的验证码
$chars='0123456789'; break;
default :
$chars='ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789'; break;
}
$string='';
while(strlen($string)<$len)
$string.=substr($chars,(mt_rand()%strlen($chars)),1);
return $string;
}
