What kind of technology is behind this?

I'm working on a custom tees shop for a school proyect and I'm kind of lost when it comes to adding this module to my website. Basically I have a blank t-shirt and a button to upload an image. I want that image to overlap my blank t-shirt.

I'm using html5, php and javascript.

I've found several sites that do this and much more like http://ift.tt/XoN4Et

Any help is appreciated!