set h/w with no aspect ratio<br />
<img src="thumb.php?i=6936.jpg&h=100&w=100" alt="" /><br /><br />

scale automatically until reaching preset max width while keeping aspect ratio<br />
<img src="thumb.php?i=6936.jpg" alt="" /><br /><br />

scale automatically until reaching user defined max width while keeping aspect ratio<br />
<img src="thumb.php?i=6936.jpg&max=300" alt="" /><br /><br />