1. A method for extracting image information from images of a target object in an optical coherence tomography (OCT) device obtained via scanning a reference path length relative to a signal path length of a signal path in the interferometer of the OCT device where the target object is located at one end of the signal path, comprising: obtaining different OCT images of the target object under different reference path lengths; processing the different OCT images to obtain a derivative with respect to the signal path length of image information of the different images; and processing the derivative to extract improved image information of the target object to reduce an effect of a signal decay due to scattering of light in the target object.