The actor signs a contract with the studio before filming. In that contract it stipulates that their likeness is signed across for all publicity, marketing and merchandise. It has to be clearly the actor in that character role. So, Emma Watson as Hermione Granger, and in her relevant costumes etc. They don't have the rights to the actor's face alone, just as that character - the whole figure.
Each movie has a contract, but some are multi-movie contracts with a "catch-all".
Dave mentioned in another thread that the actors get approval of merchandise (saying that Emma gave notes on the Yule Ball), which I have never heard of before in any contract, so I can't comment.
Star Ace would've signed a licensing deal with WB and WB would then state what they can and can't do. WB would then get final approval and would need to sign off, allowing Star Ace to then produce the figures for the market place.
