An image processing system in which a marker having a plane indicator is used to recognize the position and posture of a camera relative to the marker, the marker further having one three -dimensional indicator that has a predetermined height being located at a position predetermined relative to the plane indicator on the marker, the system comprising: a first estimation means configured to compare the location of the plane indicator extracted from the image of the camera with the predetermined location of the plane indicator to thereby estimate the position and posture P i of the camera relative to the marker; a second estimation means configured to estimate, based on the location and height of the three - dimensional indicator as well as the position of the camera relative to the marker estimated by the first estimation means, the center positions P t,estimated, P b,estimated of an upper face and a lower face of the three - dimensional indicator in the image of the camera; a detection means configured to detect, based on the image of the camera, the center position P t,detected of the upper face of the three - dimensional indicator; a determination means configured to compare the center position P t,estimated of the upper face of the three - dimensional indicator estimated by the second estimation means with the center position P t,detected of the upper face of the three - dimensional indicator detected by the detection means based on each of vectors Ve, Vd from the center position P b,estimated of the lower face of the three - dimensional indicator estimated by the second estimation means as an origin to each of the center positions P t,estimated, P t,detected of the upper face of the three - dimensional indicator to determine, when the error between vectors Ve, Vd has a value equal to or higher than a predetermined value, that the posture of the camera relative to the marker estimated by the first estimation means is false; and a calculation means which, when the false determination is made by the determination means, is configured to invert respective signs of a visual-line angle θ VXC around an X axis and a visual-line angle θ VYC around an Y axis of the camera based on the posture estimated by the first estimation means, so that the posture of the camera relative to the marker estimated by the first estimation means is corrected by subjecting it to a rotational transformation to thereby recalculate the posture of the camera relative to the marker, wherein the X axis and the Y axis respectively represent coordinate axes orthogonal to each other on the marker plane at a three-dimensional coordinate having one point on the marker as an origin. a first estimation means configured to compare the location of the plane indicator extracted from the image of the camera with the predetermined location of the plane indicator to thereby estimate the position and posture P i of the camera relative to the marker; a second estimation means configured to estimate, based on the location and height of the three - dimensional indicator as well as the position of the camera relative to the marker estimated by the first estimation means, the center positions P t,estimated, P b,estimated of an upper face and a lower face of the three - dimensional indicator in the image of the camera; a detection means configured to detect, based on the image of the camera, the center position P t,detected of the upper face of the three - dimensional indicator; a determination means configured to compare the center position P t,estimated of the upper face of the three - dimensional indicator estimated by the second estimation means with the center position P t,detected of the upper face of the three - dimensional indicator detected by the detection means based on each of vectors Ve, Vd from the center position P b,estimated of the lower face of the three - dimensional indicator estimated by the second estimation means as an origin to each of the center positions P t,estimated, P t,detected of the upper face of the three - dimensional indicator to determine, when the error between vectors Ve, Vd has a value equal to or higher than a predetermined value, that the posture of the camera relative to the marker estimated by the first estimation means is false; and a calculation means which, when the false determination is made by the determination means, is configured to invert respective signs of a visual-line angle θ VXC around an X axis and a visual-line angle θ VYC around an Y axis of the camera based on the posture estimated by the first estimation means, so that the posture of the camera relative to the marker estimated by the first estimation means is corrected by subjecting it to a rotational transformation to thereby recalculate the posture of the camera relative to the marker, wherein the X axis and the Y axis respectively represent coordinate axes orthogonal to each other on the marker plane at a three-dimensional coordinate having one point on the marker as an origin.