During one of my online window shopping (if such a thing actually exists), I saw this Piazza Sempione hand painted dress, and the more I was looking at it, the more I was thinking: ok, that shouldn't take more than 5 minutes, I mean, look at it...
--> All you need:
* white t-shirt
* fabric paint in your choice (I used a military green)
* wide paintbrush (1" to 1-1/2")
* stretch your shirt onto a cardboard covered in saran wrap or a plastic bag
* mix the fabric paint in 2/3 paint, 1/3 water (it helps with the long strokes)
* print out the picture of the dress, so you sort of have a pattern to follow
* dip your paintbrush in the paint, and with a firm hand and long strokes paint few lines.
* THAT'S IT!
* let it dry and press it on reverse to fix the color.