To get this extra functionality I added two packages to my composer.json. [...] The first is Upload by Josh Lockhart (who built Slim and started PHP The Right Way). It's currently very basic as it's not been alive long, but for the job I needed to do it worked perfect.

The second package is the ImageWorkshop that let him easily resize the uploaded images and add a watermark to the corner. He also points out that this method of pulling together packages, each with their own specializations, is the "early days of a PHP renaissance" in how people will work with the language.