Clone

<?php
$cmd = "input.jpg \( +clone -resize 600x600 -write first_save.jpg +delete \)".
" -resize 60x60 thumbnail.jpg ";
exec("convert $cmd");
?>

This code reads in the image, copys it with +clone, resizes and saves it. Then resizes and saves the next size. The part of the code within the \( \) has no effect on any of the other part of the code.