Valdes GK def
pique, Mascherano CB Def
Alba, FB def
Alves, WB Attack, wide play hug touchline
Busquets, Anchor man def
Xavi, DLP support
Iniesta, CM support
Messi Trequartista?!?
Pedro, Winger Attack, Wide play hug touchline
Villa, poacher/advanced forward.
This would be my guess based on those positions however it would all depend on how the team played outside of one still image...