1. An image processing apparatus for acquiring a shape of a target object contained in a series of moving pictures, comprising: an image capture unit configured to take in time-series images obtained in time series by shooting a target object; a feature point extraction unit configured to extract feature points of said target object from said time-series images taken in by said image capture unit; a motion information extraction unit configured to determine a change of a position and posture of said target object in each point of time in said time-series images by correlating feature points contained in the image at a point of time with those at another point of time in said time-series images extracted by said feature point extraction unit to obtain correlated feature points, and configured to analyze positional coordinate information on the correlated feature points; an inter-image linear combination coefficient calculating unit configured to calculate a linear combination coefficient of image luminance between said time-series images by analyzing information on luminance at the feature points correlated by said motion information extraction unit and luminance around the correlated feature points; and a distance information detecting unit configured to estimate information on a distance to each point of said target from the position and posture of said target object determined by said motion information extraction unit at each point of time in said time-series images and the linear combination coefficient of image luminance between said time-series images, the linear combination coefficient being calculated by said inter-image linear combination coefficient calculating unit.