Add the following lines to your deps file:
[PhpThumb]
git=http://github.com/tvogels/phpthumb.git
target=phpthumb
And those to app/autoload.php:
$loader->registerPrefixes(array(
...
'PhpThumb_' => __DIR__.'/../vendor/phpthumb/lib',Now run php bin/vendors update or php bin/vendors install.
$thumb = \PhpThumb_Factory::create(...);