Hey Agd, that is a cool painting. I used to work with a guy that did this professionally and there is a spray paint booth next to my airbrush kiosk in Las Vegas.
Guys this painting is 100% legit. the way that it is down is with different effects, tricks and free hand shields. for example the stars are down by making the spray paint can sputter. the moon is down with a shield and a "marbalizing technique"
I believe that you can watch videos of this on youTube just look under spraypaint art. you can create some amazing paintings with it.