1. A method for CT image correction, the method comprising: obtaining contour data of a scanned subject; reconstructing a shape image of the scanned subject according to the contour data, wherein the contour data of the scanned subject is obtained by scanning the scanned subject through visual equipment; obtaining original CT projection data of the scanned subject; and reconstructing a CT image according to the original CT projection data; determining an image of a supervision field by performing image matching between the shape image and the CT image of the scanned subject; obtaining supervision field projection data, and using the supervision projection data to correct the CT image; placing a positioning assisting device on the scanned subject, wherein the positioning assisting device assists the image matching of the shape image and the CT image; wherein performing an image matching between the shape image and the CT image of the scanned subject when the visual equipment is not mounted on the gantry of the CT device comprises: providing the shape image and the CT image of the scanned subject, respectively; performing image segmentation on the shape image for screening out a corresponding first image of the positioning assisting device in the shape image; screening out, from the CT image, a corresponding second image of the positioning assisting device in the CT image; extracting a predetermined characteristic of the first image and a predetermined characteristic of the second image, respectively; implementing the image matching of the shape image and the CT image of the scanned subject by performing a characteristic matching on the predetermined characteristic of the first image and the predetermined characteristic of the second image; wherein performing a characteristic matching on the predetermined characteristic of the first image and the predetermined characteristic of the second image comprises: setting the predetermined characteristic of the first image to form a first predetermined pattern, and setting the predetermined characteristic of the second image to form a second predetermined pattern; calculating a rotation-and-translation matrix according to the first predetermined pattern and the second predetermined pattern, wherein the rotation-and-translation matrix is used to convert the first predetermined pattern to the second predetermined pattern; and implementing the characteristic matching of the predetermined characteristic of the shape image and the predetermined characteristic of the CT image by performing a spatial transformation on the shape image based on the rotation-and-translation matrix.