thanks for your reply..
for a project like this one, we feel that a physical model representing the whole scenario would be sufficient.. so by slowly rolling a small ball over a line(having detectors and thick width) and the ball being tagged in the same ways as the goods are tagged to prevent...
we are planning to do a project which is related to soccer.. the aim here is to detect whether the ball has crossed the goalline or not.. we believe that the basic idea of using line detectors will work only if we are able to differentiate between the ball crossing the line or any other...