Speed up jpg resize

<?php 
exec("convert -size 250x90 input.jpg -resize 250x90 output.jpg");

// Later versions of Imagemagick use this instead:

exec("convert -define jpeg:size=250x90 input.jpg -resize 250x90 output.jpg");

?>

Defining the size of the jpg when loading it will speed up the resizing process. This is done by adding the -size option.