<?php 

$w_new = '100'; 

$foto = 'foto.jpg'; 

$old = imageCreateFromJpeg("$foto"); 

$w = imageSX($old); 

$h = imageSY($old); 

$new = $h / $w; 

$h_new= $w_new * $new; 

$new = imageCreate($w_new, $h_new); 

$new = imagecreatetruecolor($w_new, $h_new); 

imageCopyResized($new, $old, 0, 0, 0, 0, $w_new, $h_new, $w, $h); 

imageJpeg($new,"","80"); 

?>