1. A method for real-time obstacle detection from a vehicle moving relative to a road, comprising: calibrating an image capturing device, such that any image point can be mapped to a real-world point; receiving one or more images from the image capturing device; receiving information about the ego-motion of the image capturing device; selecting one or more real-world points according to a tractability criterion; applying a motion estimation method on the one or more real-world points, the one or more images, and the known plane to determine an image motion flow of the one or more real-world points; determining a true motion flow of the one or more real-world points based on the one or more real world points, the one or more images, and the ego-motion; and determining that the one or more real-world points is one or more obstacle points by comparing the image motion flow and the true motion flow.