Automotive tire tread depth has a major influence on a car's safety and thus has to be closely monitored. However, there is currently no on-board solution that can measure tire wear with an accuracy of less than 1 mm. TireEye is an optical device mounted inside the wheel well and facing towards the road. It records the cross-section of the longitudinal tread groove and extracts its outline by means of adaptive Canny edge detection. The tread wear indicators serve es means to calibrate the scale since they provide the minimum tread depth.