php 绘制验证码 示例

 <?php
 header("content-type:image/jpeg");

 session_start();//开启session

 //宽高 字体大小
 $width=120;
 $height=40;
 $fontsize=20;

 //给画布宽高
 $img=imagecreatetruecolor($width,$height);

 //画布背景色
 $bgcolor=imagecolorallocate($img,rand(200,255),rand(200,255),rand(200,255));

  //画布边框背景
 $bordercolor=imagecolorallocate($img,rand(0,155),rand(0,155),rand(0,155));

 //内容字体颜色
 $fontcolor=imagecolorallocate($img,rand(30,100),rand(30,100),rand(30,100));

 //填充背景色
 imagefill($img,0,0,$bgcolor);

 //填充边框
 imagerectangle($img,0,0,$width-1,$height-1,$bordercolor);

 //干扰点
 for($a=0;$a<100;$a++){
     imagesetpixel($img,rand(1,$width-2),rand(1,$height-2),$bordercolor);
 }

 //创建数组
 $shuzi=range(0,9);

 //随机数
 $suiji=$shuzi[rand(0,count($shuzi)-1)].$shuzi[rand(0,count($shuzi)-1)]
     .$shuzi[rand(0,count($shuzi)-1)].$shuzi[rand(0,count($shuzi)-1)];

 //输出内容
 imagettftext($img,$fontsize,rand(-5,5),rand(15,25),rand(28,33),$fontcolor,'ziti.ttf',$suiji);$_SESSION['yzm_b']=$suiji;

 //获取‘验证码输入框的内容’

 //输出画布
 imagejpeg($img);
 ?>