The line tracking module contains photoresistors that can detect a white line from a black surface, or vice versa.

This is the last failed attempt, with a high expectation of success. Although it did not, but it is worth to remember.

An improved version:

PS: The testing track was built using painted cardboard boxes, so it can be folded and moved around easily. Here are some pictures recording the fun/miserable(depending on who you ask in the team) time of building it.