A computerized method performable at night by a driver assistance system mountable in a host vehicle while the host vehicle is moving forward with headlights on, wherein the driver assistance system includes a camera operatively connectible to a processor, the method including the steps of: capturing a first image frame and a second image frame of a road in the field of view of the camera; processing said first image frame and said second image frame to locate a first dark image patch of said first image frame and a second dark image patch of said second image frame; tracking said first and said second dark image patches (1107, 1111) from said first image frame to said second image frame as corresponding image portions of the same portion of the road; and measuring respective thicknesses in vertical image coordinates of said first and second dark image patches (1107, 1111) responsive to said tracking from said first image frame to said second image frame; determining that a change of said thicknesses between said first and second dark image patches (1107, 1111) is consistent with a shadow cast by an obstacle in the road from illumination from the headlights, wherein for Z L << Z T for distance Z L between camera and headlights and distance Z T between the headlights and the obstacle, said thickness in the images changes as a function of 1/ Z T and is modeled by a first function of the focal length of the camera, the difference in heights between the camera and the headlights, the distance Z T and the height of the camera, thereby detecting said obstacle in the road; or determining that a change of said thicknesses between said first and second dark image patches (1107, 1111) is not consistent with a shadow cast by an obstacle from illumination from the headlights and is consistent with a dark patch in the road, wherein said thickness in the images changes as a function of 1/Z 2 S1, Z S1 being the distance to the dark patch in the road, and is modeled by a second function, different from the first function, wherein the second function includes the focal length of the camera, height of the camera Hc, the distance Z S1 and α, wherein α = Z S2 - Z S1 and the dark patch on the road at a given time stretches from Z S1 to Z S2. capturing a first image frame and a second image frame of a road in the field of view of the camera; processing said first image frame and said second image frame to locate a first dark image patch of said first image frame and a second dark image patch of said second image frame; tracking said first and said second dark image patches (1107, 1111) from said first image frame to said second image frame as corresponding image portions of the same portion of the road; and measuring respective thicknesses in vertical image coordinates of said first and second dark image patches (1107, 1111) responsive to said tracking from said first image frame to said second image frame; determining that a change of said thicknesses between said first and second dark image patches (1107, 1111) is consistent with a shadow cast by an obstacle in the road from illumination from the headlights, wherein for Z L << Z T for distance Z L between camera and headlights and distance Z T between the headlights and the obstacle, said thickness in the images changes as a function of 1/ Z T and is modeled by a first function of the focal length of the camera, the difference in heights between the camera and the headlights, the distance Z T and the height of the camera, thereby detecting said obstacle in the road; or determining that a change of said thicknesses between said first and second dark image patches (1107, 1111) is not consistent with a shadow cast by an obstacle from illumination from the headlights and is consistent with a dark patch in the road, wherein said thickness in the images changes as a function of 1/Z 2 S1, Z S1 being the distance to the dark patch in the road, and is modeled by a second function, different from the first function, wherein the second function includes the focal length of the camera, height of the camera Hc, the distance Z S1 and α, wherein α = Z S2 - Z S1 and the dark patch on the road at a given time stretches from Z S1 to Z S2.