The present invention provides an image processing method which can search, at high speed, for image coordinates of a pixel corresponding to a position whose three-dimensional position is known, with respect to a line sensor image in which a surface of an object (i.e. the earth) is continuously taken by a line sensor mounted on a flight vehicle. The method includes calculating coordinates transformation information that is transformation information from an image coordinates system to a three-dimensional reference coordinates system for each line of a line sensor image, searching for a line where a distance between a line sensor view for each line that is calculated using flight vehicle three-dimensional coordinates position/speed information and the coordinates transformation information for each line of a line sensor image and a point whose three-dimensional position is known is smallest as the most suitable line corresponding to the point whose three-dimensional position is known on a three-dimensional coordinates, and determining a pixel where a distance between a straight line calculated by using flight vehicle three-dimensional coordinates position/speed information and the coordinates transformation information for each line with respect to each pixel on a line that is searched for as the most suitable line and the point whose three-dimensional position is known is smallest as image coordinates of a pixel on the line sensor image corresponding to the point whose three-dimensional position is known.