ImageGen is a powerful plugin that allows you to manipulate the images on the templates of Umbraco pages. From the project's website:
"With more than 30 options, ImageGen can create hundreds of thousands of variations to meet virtually any need. ImageGen is easy to install and use on your website. ImageGen creates extremely high-quality images quickly. And ImageGen’s advanced caching means images are served immediately for fast and responsive websites."
Using The Plugin
Using the plugin is as simple as passing a string to the imagegen.ashx: