Interactive Advertising

I'd like to invent an advertising system which can identify the audience in the area and play appropriate ads for this group.  This would be ideal for airports or other large areas where the general audience is known but the specific groups within it are not.  Additionally this system could go a step further and communicate with the people watching the ad.  This would be particularly useful in airports when patrons are standing on moving sidewalks.  When the person gets on the moving sidewalk it will identify who the person is (age, gender, race, etc.) and play an ad of a person walking next to them (on a screen) which best advertises to that group.