PHP实现即时网站截图

<form action="screenshot_it.php">网站地址 (不带 http://):
<br /><input name="site" type="text" size="15" value="www."/>
<br/>大小: <br /><input name="x" type="text" value="800" size="3"/>x<input name="y" type="text" value="1000" size="3"/>px<br />
图片格式:<br /><select name="format"> <option value="PNG">PNG</option>  <option value="JPEG">JPEG</option> </select> 
<br /><br /><input type="submit" name="preview" value="生成截图"/></form>

<?php
$x = $_REQUEST['x'];
$y = $_REQUEST['y'];
$format = $_REQUEST['format'];
$site = $_REQUEST['site'];
$surl = 'http://0907.org/screenshot/screenshot_it.php?site='.$site.'&x='.$x.'&y='.$y.'&format='.$format;
if($_REQUEST['format'] == 'PNG') {
$ifm = 'png';
} else {
$ifm = 'jpg';
}
$imt = 'image/'.$ifm;
$ifn = 'screenshot.'.$ifm;
if(isset($_REQUEST['preview'])) {
$iurl = 'http://域名/子目录/screenshot_it.php?site='.$site.'&x='.$x.'&y='.$y.'&format='.$format; 
//例如：http://0907.org/screenshot/screenshot_it.php?site='.$site.'&x='.$x.'&y='.$y.'&format='.$format;
$gwptitle = $_REQUEST['site'].' blog.0907.org';
include_once("../css.php");   
//这里可以删除呦！因为是CSS

echo '<div>';
echo '&raquo; <b>点击图片下载截图！</div></b><br/><a href="'.$iurl.'"><img src="'.$iurl.'" width="240" height="320" /></a><br />';
} else {
header("Content-type: $imt");
header("Content-Disposition: attachment; filename= $ifn");
readfile($surl);
}
?>