A computer implemented method in a Computed Tomography "CT" system for security check, comprising steps of: reading inspection data of an inspected object; inserting at least one three-dimensional "3D" Fictional Threat Image "FTI" into a 3D inspection image of the inspected object, wherein the 3D inspection image is obtained from the inspection data; wherein the method is characterized by further comprising steps of: receiving a selection of at least one region in the 3D inspection image including the 3D FTI; and providing a feedback of whether the 3D inspection image includes at least one 3D FTI in response to the selection, wherein selection of at least one region comprises selection of a part of the displayed 3D inspection image at at least two different angles of view, wherein the at least two different angles of view are substantially orthogonal to each other, transparent regions are removed from the inspection data to obtain a hierarchical bounding box of opaque regions in the inspection data, and then a scene depth is rendered for the hierarchical bounding box to obtain a depth map on the front side and a depth map on the back side, and wherein the step of providing a feedback of whether the 3D inspection image includes at least one 3D FTI in response to the selection comprises: performing retrieval in the depth map on the front side and the depth map on the back side respectively according to a region selected by a user at a first angle of view to generate a first bounding box; performing ray casting with the generated first bounding box as a volume texture carrier; performing retrieval in the depth map on the front side and the depth map on the back side respectively according to a region selected by the user at a second angle of view substantially orthogonal to the first angle of view, to generate a second bounding box; performing a Boolean intersection operation on the first bounding box and the second bounding box in an image space, to obtain a marked region in a 3D space as at least one selected region; and judging whether the at least one selected region includes the at least one 3D FTI. reading inspection data of an inspected object; inserting at least one three-dimensional "3D" Fictional Threat Image "FTI" into a 3D inspection image of the inspected object, wherein the 3D inspection image is obtained from the inspection data; receiving a selection of at least one region in the 3D inspection image including the 3D FTI; and providing a feedback of whether the 3D inspection image includes at least one 3D FTI in response to the selection, wherein selection of at least one region comprises selection of a part of the displayed 3D inspection image at at least two different angles of view, wherein the at least two different angles of view are substantially orthogonal to each other, transparent regions are removed from the inspection data to obtain a hierarchical bounding box of opaque regions in the inspection data, and then a scene depth is rendered for the hierarchical bounding box to obtain a depth map on the front side and a depth map on the back side, and wherein the step of providing a feedback of whether the 3D inspection image includes at least one 3D FTI in response to the selection comprises: performing retrieval in the depth map on the front side and the depth map on the back side respectively according to a region selected by a user at a first angle of view to generate a first bounding box; performing ray casting with the generated first bounding box as a volume texture carrier; performing retrieval in the depth map on the front side and the depth map on the back side respectively according to a region selected by the user at a second angle of view substantially orthogonal to the first angle of view, to generate a second bounding box; performing a Boolean intersection operation on the first bounding box and the second bounding box in an image space, to obtain a marked region in a 3D space as at least one selected region; and judging whether the at least one selected region includes the at least one 3D FTI. performing retrieval in the depth map on the front side and the depth map on the back side respectively according to a region selected by a user at a first angle of view to generate a first bounding box; performing ray casting with the generated first bounding box as a volume texture carrier; performing retrieval in the depth map on the front side and the depth map on the back side respectively according to a region selected by the user at a second angle of view substantially orthogonal to the first angle of view, to generate a second bounding box; performing a Boolean intersection operation on the first bounding box and the second bounding box in an image space, to obtain a marked region in a 3D space as at least one selected region; and judging whether the at least one selected region includes the at least one 3D FTI.