php gd实现下载图片

<?php
header("Content-type:text/html ; charset=utf-8");
 
if (!empty($_POST['submit'])){
	$url = $_POST['url'];
	$pictureName = $_POST['pictureName'];
	$img = getPicture($url,$pictureName);
	echo '<pre><img src="'.$img.'"></pre>';
	}
function getPicture($url,$pictureName){
	if ($url == "") return false;
	//获取图片的扩展名
	$info = getimagesize($url);
	$mime = $info['mime'];
	$type = substr(strrchr($mime,'/'), 1);
	//不同的图片类型选择不同的图片生成和保存函数
	switch($type){
		case 'jpeg':
			$img_create_func = 'imagecreatefromjpeg';
			$img_save_func = 'imagejpeg';
			$new_img_ext = 'jpg';
			break;
		case 'png':
			$img_create_func = 'imagecreatefrompng';
			$img_save_func = 'imagepng';
			$new_img_ext = 'png';
			break;
		case 'bmp':
			$img_create_func = 'imagecreatefrombmp';
			$img_save_func = 'imagebmp';
			$new_img_ext = 'bmp';
			break;
		case 'gif':
			$img_create_func = 'imagecreatefromgif';
			$img_save_func = 'imagegif';
			$new_img_ext = 'gif';
			break;
		case 'vnd.wap.wbmp':
			$img_create_func = 'imagecreatefromwbmp';
			$img_save_func = 'imagewbmp';
			$new_img_ext = 'bmp';
			break;
		case 'xbm':
			$img_create_func = 'imagecreatefromxbm';
			$img_save_func = 'imagexbm';
			$new_img_ext = 'xbm';
			break;
		default:
			$img_create_func = 'imagecreatefromjpeg';
			$img_save_func = 'imagejpeg';
			$new_img_ext = 'jpg';					
	}
	if ($pictureName == ""){
		$pictureName = time().".{$new_img_ext}";
	}else{
		$pictureName = $pictureName.".{$new_img_ext}";
	}
	$src_im = $img_create_func($url); //由url创建新图片
	$img_save_func($src_im, $pictureName); //输出文件到文件
	return $pictureName;
}
 
?>
<form method="POST" action="">
远程url地址：<input type="text" name="url" size=20 /><br />
文件名称：<input type="text" name="pictureName" size=20 />
<input type="submit" name="submit" value="下载" />
</form>