The images bear a European ratings logo on them, so, even if they're real, there's a chance the rest of the world could be getting the game some other season.
But these posters have the benefit of plausibility. GTA V was shown in action to reporters from Game Informer magazine earlier this month. And, from personal experience, I can say that Rockstar tends not to show reporters their games more than six or so months before release. Autumn seems like a good time to launch.
So... legit? You decide (or, Rockstar, tell us, please!).
Premiera GTA V wiosną 2013! Mamy przeciek! TYLKO U NAS! [GTA-V.pl, Thanks to everyone who sent this in!]