A method for determining the distance from a tip of a pointer to a surface using a light source and a single camera, the method comprising detecting in an image captured by the camera a tip of the pointer, determining in the image captured by the camera the intensity of a set of pixels below the tip of the pointer, the intensity defining a reflection by the surface of the tip of the pointer illuminated by the light source, and determining the distance from the tip of the pointer to the surface depending upon the intensity of the set of pixels below the tip of the pointer and an intensity of pixels of the tip of the pointer in the image.