i needed the ability to grab the mod time of an image on a remote site. the following is the solution with the help of Joe Ferris.
<?php
function filemtime_remote($uri)
{
 $uri = parse_url($uri);
 $handle = @fsockopen($uri['host'],80);
 if(!$handle)
 return 0;
 fputs($handle,"GET $uri[path] HTTP/1.1\r\nHost: $uri[host]\r\n\r\n");
 $result = 0;
 while(!feof($handle))
 {
 $line = fgets($handle,1024);
 if(!trim($line))
 break;
 $col = strpos($line,':');
 if($col !== false)
 {
 $header = trim(substr($line,0,$col));
 $value = trim(substr($line,$col+1));
 if(strtolower($header) == 'last-modified')
 {
 $result = strtotime($value);
 break;
 }
 }
 }
 fclose($handle);
 return $result;
}
// echo filemtime_remote('http://www.somesite.com/someimage.jpg');
?>