An image processing apparatus, which processes an image of a tomogram obtained by capturing an image of an eye to be examined by a tomography apparatus, comprising: layer candidate detection means for detecting layer candidates of a retina of the eye to be examined from the tomogram; artifact region determination means for determining an artifact region in the tomogram based on image features obtained using the layer candidates; and layer decision means for deciding a position of a layer of the retina in the artifact region, based on a determination result of said artifact region determination means, wherein said layer decision means is configured to use a geometric model which is used to specify a layer geometry included in the artifact region and is defined by a plurality of control points, and decide the position of the layer based on evaluation functions associated with a geometry of the geometric model and evaluation functions associated with intensities near the control points, and wherein said artifact region determination means is configured to: extract a blood vessel region and/or an exudates region from a projection image generated from the tomogram by projecting the tomogram in a direction of a z-axis and to back-project the blood vessel region and/or the exudates region onto the tomogram, wherein said artifact region determination means is configured to identify the artifact region based on a continuity of layer candidate points of a layer candidate detected in the tomogram, wherein the continuity of layer candidate points is calculated not for all layer candidate points, but for the interior of the back-projection region and in the vicinity of the region in x-y directions. layer candidate detection means for detecting layer candidates of a retina of the eye to be examined from the tomogram; artifact region determination means for determining an artifact region in the tomogram based on image features obtained using the layer candidates; and layer decision means for deciding a position of a layer of the retina in the artifact region, based on a determination result of said artifact region determination means, wherein said layer decision means is configured to use a geometric model which is used to specify a layer geometry included in the artifact region and is defined by a plurality of control points, and decide the position of the layer based on evaluation functions associated with a geometry of the geometric model and evaluation functions associated with intensities near the control points, and wherein said artifact region determination means is configured to: extract a blood vessel region and/or an exudates region from a projection image generated from the tomogram by projecting the tomogram in a direction of a z-axis and to back-project the blood vessel region and/or the exudates region onto the tomogram, wherein said artifact region determination means is configured to identify the artifact region based on a continuity of layer candidate points of a layer candidate detected in the tomogram, wherein the continuity of layer candidate points is calculated not for all layer candidate points, but for the interior of the back-projection region and in the vicinity of the region in x-y directions. extract a blood vessel region and/or an exudates region from a projection image generated from the tomogram by projecting the tomogram in a direction of a z-axis and to back-project the blood vessel region and/or the exudates region onto the tomogram, wherein said artifact region determination means is configured to identify the artifact region based on a continuity of layer candidate points of a layer candidate detected in the tomogram, wherein the continuity of layer candidate points is calculated not for all layer candidate points, but for the interior of the back-projection region and in the vicinity of the region in x-y directions.