Photographia is a “ready to use” PHP script using the GD library which allows you (or your users) to upload jpg, gif or png images, apply effects and then open the image in a new window so you (or the user) can save it. It features 18 filters but you can add as many as you want by editing the html code or editing the json file.
Photographia is mobile friendly and features an extensive documentation.
PHP5 and GD are required.