My guess is that it's a production control feature, not a security feature at all. If it were for security purposes, you would want one image to represent a 'genuine chip'. A dozen or more would only confuse any security personnel scanning them. Probably something to do with tracking production lots.

It's also possible that they are testing fluorescent ink for some future use... kind of like the multiple stripes you sometimes see on the highway with a sign that says 'paint test'. They may be looking to see how well it survives handling by players and friction in and out of chip trays.