This picture made me FREAKING CRY :'( It's so true... he was so brave. And some might say he was sorted into the wrong House, but he was probably as difficult to Sort as Harry, if not more. He was determined, ambitious, cunning, and had bad intentions at first... and was also extremely brave and willing to die for what he loved, VERY loyal, and was freakin' genious. I mean, he invented his own spells! And for them to work, you didn't even have to know what they did, let alone focus.
I'm pretty sure the picture is from The Half-Blood Prince, when Snape is about to kill Dumbledore. I think it conveys perfectly the emotions he's going through not just then, but all through the series. So sad...