Yeah the image is horrible big, I know. Basically people think those are the concept art for the classes. So far they've been right if you look at the main website.

Right now the revealed classes are:
Elementalist (fireballs, lightning bolts etc) - The bottom image obviously.
Warrior (Swords and stuff) - the golden image.
Ranger (Pets and bows) - the green image.

The grey image suggests the Assassin is back. The purple one the Mesmer and the blue one some sort of Cleric/Paladin, or basically a heavily armoured holy warrior class. That leaves two unknown professions but the guess is necromancer and probably an engineer type. Of course this is all pure speculation.

So there you go DK.