Structure laser Sensor + custom software.
Tip 1: For your information you don't need the laser, it has other way to replace the laser. note:we try laser is one of the solution but not the best solution.
Tip 2: You can use other way like the structure logic please study the 123Catch app in iOS, android and window. that is using image color to find out the image highlight and shadow, please take a look the open source project openCV this is super easy project and a lot resource in different language.