Display image without saving

<?php  
$cmd = "convert input.jpg -gravity Center -crop 100x100+0+0  JPG:-"; 
header("Content-type: image/jpeg"); 
passthru($cmd, $retval); 
?>  

This reads the image, crops to a 100px wide x 100px heigh section in the middle then displays it. This must be on a page of its own and is called where you want it with the standard image tags using the page name as the image name.