An image processing apparatus which processes a plurality of tomograms (Tp, Tq) obtained by acquiring a plurality of tomograms (T1, T2,..., Tn) each including a section (x-z) along a thickness direction (z) of a retina, comprising: acquisition means for acquiring pieces of structure information about a layer structure of the retina from image information (PM1, PS1, PM2, PS2) of respective lines of the tomograms along the thickness direction; and appending means for appending the acquired pieces of structure information (D1, D5) to the respective lines; wherein said acquisition means detects, for each of the respective lines, a boundary position along the thickness direction of a predetermined layer in the retina based on the image information of the line and acquires, as one of the pieces of structure information for that line, an artifact attribute representing that an artifact exists in the image information of that line if said acquisition means has not detected the boundary of the predetermined layer and an artifact attribute representing that no artifact exists in the image information of that line if said acquisition means has detected the boundary of the predetermined layer; characterized by mapping means for mapping the acquired pieces of structure information of the respective lines of the plurality of tomograms to positions corresponding to the respective lines in a plane (x-y) crossing the thickness direction at a right angle so as to generate a two-dimensional map with artifact areas indicating positions in said plane corresponding to lines of the plurality of tomograms to which the artifact attribute representing that an artifact exists is appended; and determining means for determining, for each artifact area (SR1, SR2) in the two-dimensional map, a cause of the artifact based on one of a size and shape of the artifact area. acquisition means for acquiring pieces of structure information about a layer structure of the retina from image information (PM1, PS1, PM2, PS2) of respective lines of the tomograms along the thickness direction; and appending means for appending the acquired pieces of structure information (D1, D5) to the respective lines; wherein said acquisition means detects, for each of the respective lines, a boundary position along the thickness direction of a predetermined layer in the retina based on the image information of the line and acquires, as one of the pieces of structure information for that line, an artifact attribute representing that an artifact exists in the image information of that line if said acquisition means has not detected the boundary of the predetermined layer and an artifact attribute representing that no artifact exists in the image information of that line if said acquisition means has detected the boundary of the predetermined layer; characterized by mapping means for mapping the acquired pieces of structure information of the respective lines of the plurality of tomograms to positions corresponding to the respective lines in a plane (x-y) crossing the thickness direction at a right angle so as to generate a two-dimensional map with artifact areas indicating positions in said plane corresponding to lines of the plurality of tomograms to which the artifact attribute representing that an artifact exists is appended; and determining means for determining, for each artifact area (SR1, SR2) in the two-dimensional map, a cause of the artifact based on one of a size and shape of the artifact area.