<?php if(!isset($_SESSION)){ //判断session是否开启    session_start(); } 
/**随机生成验证码函数*param $m：验证码位数 默认值为4*param $type:验证码类型 0：数学 1：数字+小写字母 2：数字+大小写字母*/function getCode($m=4,$type=0){    $str = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";    $t = array(9,35,strlen($str)-1);//t[0]:0-9:数字 ;t[2]:0-35：数字+小写字母 ;t[2]:0-最后：所有字符;    $c ="";    for($i=0; $i<$m; $i++){        $c.=$str[rand(0,$t[$type])];    }    return $c;}//1.获取验证码字符$num=4;$str = getCode($num,0);$_SESSION['verifycode'] = $str;//2.创建画布$width=$num*20;$height=30;$im = imagecreatetruecolor($width,$height);$c = imagecolorallocate($im,111,0,55);$rect = imagecolorallocate($im,20,0,190);$bg = imagecolorallocate($im,200,200,200);//3.开始绘制imagefill($im,0,0,$bg);//背景色imagerectangle($im,0,0,$width-1,$height-1,$rect);//边框//4.添加干扰点for($i=0; $i<200; $i++){    $c = imagecolorallocate($im,rand(0,255),rand(0,255),rand(0,255));    imagesetpixel($im,rand(0,$width),rand(0,$height),$c);}//5.添加干扰线for($i=0; $i<5; $i++){    $c = imagecolorallocate($im,rand(0,255),rand(0,255),rand(0,255));    imageline($im,rand(0,$width),rand(0,$height),rand(0,$width),rand(0,$heigth),$c);}//6.绘制验证码内容for($i=0; $i<$num; $i++){    imagettftext($im,18,8+(10*$i),8+(18*$i),24,$c,"plantc.ttf",$str[$i]);//plantc.ttf为字体文件，根据实际路径设置}
//7.输出验证码图形header("Content-Type:image/png");imagepng($im);imagedestroy($im);?>