Hey omg! That looks so similar to my canvas pic! I made my pic using canvas and then edited it using this website canva.com. You can see some of my very noobish work here http://codepen.io/aqilahmisuary/ but yeah so sorry I didn't steal your pic, all the pics on the github blog are either stock pics or our own. However your stuff are pretty amazing! You should make tutorials! =)
I've just been following this tutorial http://cssdeck.com/labs/lets-make-a-bouncing-ball-in-html5-canvas and then experimenting with the code.