A computer-implemented method of annotating road scene images, the method comprising implementing, at an image processing system, the following steps: receiving a time sequence of two dimensional images as captured by an image capture device of a travelling vehicle; processing the images to reconstruct, in three-dimensional space, a path travelled by the vehicle; using the reconstructed vehicle path to determine, in three-dimensional space, expected road structure extending along the reconstructed vehicle path; and generating road annotation data for marking at least one of the images with an expected road structure location, by performing a geometric projection of the expected road structure in three-dimensional space onto a two-dimensional plane of that image; characterized in that the expected road structure is determined based on: i) a road normal vector n, estimated from the images as: n = 1 ∑ i = 2 N − 2 ‖ n i ‖ ∑ i = 2 N − 2 n i n i = R i − 1 m i − 1, i ⊕ m i, i + 1, Ri being a camera pose determined for image i in reconstructing the vehicle path, and m i,j being a normalised motion vector between frames i and j, and ii) a forward direction vector estimated from the images as: f = 1 ∑ i a i ∑ i = 2 N − 2 a i f i a i = max m i − 1, i ⊤ m i, i + 1, 0 f i = R i − 1 m i − 1, i + 1, Ri being a camera pose determined for image i in reconstructing the vehicle path, m i,j being a normalised motion vector between frames i and j; wherein f and n are used to determined border points of the expected road structure as: b i left = g i + w i left R i r b i right = g i + w i right R i r r = f ⊗ n Ri being a camera pose determined for image i in reconstructing the vehicle path, gi being a road point below the image capture device, and being distances to left and right borders of a road lane in which the vehicle is travelling respectively; wherein the road point below the camera is computed as: g i = c i + h R i n wherein h is a height of the camera and c i is a 3D position of the image capture device determined in reconstructing the vehicle path. receiving a time sequence of two dimensional images as captured by an image capture device of a travelling vehicle; processing the images to reconstruct, in three-dimensional space, a path travelled by the vehicle; using the reconstructed vehicle path to determine, in three-dimensional space, expected road structure extending along the reconstructed vehicle path; and generating road annotation data for marking at least one of the images with an expected road structure location, by performing a geometric projection of the expected road structure in three-dimensional space onto a two-dimensional plane of that image; characterized in that the expected road structure is determined based on: i) a road normal vector n, estimated from the images as: n = 1 ∑ i = 2 N − 2 ‖ n i ‖ ∑ i = 2 N − 2 n i n i = R i − 1 m i − 1, i ⊕ m i, i + 1, Ri being a camera pose determined for image i in reconstructing the vehicle path, and m i,j being a normalised motion vector between frames i and j, and ii) a forward direction vector estimated from the images as: f = 1 ∑ i a i ∑ i = 2 N − 2 a i f i a i = max m i − 1, i ⊤ m i, i + 1, 0 f i = R i − 1 m i − 1, i + 1, i) a road normal vector n, estimated from the images as: n = 1 ∑ i = 2 N − 2 ‖ n i ‖ ∑ i = 2 N − 2 n i n i = R i − 1 m i − 1, i ⊕ m i, i + 1, Ri being a camera pose determined for image i in reconstructing the vehicle path, and m i,j being a normalised motion vector between frames i and j, and ii) a forward direction vector estimated from the images as: f = 1 ∑ i a i ∑ i = 2 N − 2 a i f i a i = max m i − 1, i ⊤ m i, i + 1, 0 f i = R i − 1 m i − 1, i + 1, Ri being a camera pose determined for image i in reconstructing the vehicle path, m i,j being a normalised motion vector between frames i and j; wherein f and n are used to determined border points of the expected road structure as: b i left = g i + w i left R i r b i right = g i + w i right R i r r = f ⊗ n Ri being a camera pose determined for image i in reconstructing the vehicle path, gi being a road point below the image capture device, and being distances to left and right borders of a road lane in which the vehicle is travelling respectively; wherein the road point below the camera is computed as: g i = c i + h R i n wherein h is a height of the camera and c i is a 3D position of the image capture device determined in reconstructing the vehicle path.