That was the first illustration for my very first Harry Potter fanfiction (written in Greek and waiting for some Greek-speaking volunteer to translate it in English).
Don't ask me how but Snape found himself in the students' toilets (see, the professors' toilets were being repaired or something - d'uh). Draco, thinking he was alone, went in to look at his newly-made tattoo (yes, that IS silly).
Well... one of them saw more than he should...
Draco and Snape belong to J.K. Rowling