用PHP代码在网页上生成图片

<?php
/
  Created by PhpStorm.
  User: Administrator
  Date: 2015/6/29
  Time: 21:25
 /
header('Content-type:image/png');//设置mime type
$img = imagecreate(400,300);//设置图片像素
imagecolorallocate($img,255,255,255);//给图片上色
imageellipse($img,200,200,50,50,imagecolorallocate($img,255,0,0));//在图片上绘制图形，中心点200,200；宽高50,50
imagepng($img);//设置图片格式为PNG