Range-finding method and computer program product

A range-finding method includes driving a moving member to move relative to a target to a first position, capturing a picture of the target in the first position to obtain a first picture by a picture capturing module on the moving member, feature-analyzing the first picture to obtain a first feature image of the first picture; driving the moving member to move relative to the target from the first position to a second position, capturing a picture of the target in the second position to obtain a second picture by the picture capturing module, feature-analyzing the second picture to obtain a second feature image of the second picture, and by a processing unit, computing a distance between the moving member in the second position and the target according to a distance between the first and second positions and a size change between the first and second feature images.