Is that Tom Hanks' actual face done up as a Groucho Marx-mustachioed conductor in ''The Polar Express'' (due in November)? Or is it just an incredible computer-graphic simulation? It's both, really, since director-cowriter Robert Zemeckis (''Cast Away'') is employing motion-capture technology to place Hanks inside what he calls a ''moving painting'' version of Chris Van Allsburg's award-winning 1985 picture book. Hanks didn't have to wear a conductor costume on the set -- just a leotard festooned with infrared-beam receptors and some 165 freckle-like reflective dots glued to his face. ''It's not animation,'' says Zemeckis of the results. ''It's got all the subtlety and warmth of a human performance.''