1. An image processing device comprising: derivative value calculating means for calculating a second order partial derivative matrix and at least one first order partial derivative value of a pixel value at each pixel position in an image; and evaluating means for calculating an evaluation value of a likelihood of being a line-like structure and/or an evaluation value of a likelihood of being a plate-like structure for the pixel position based on values of the second order partial derivative matrix, wherein the larger the first order partial derivative value, the smaller the evaluation values outputted by the evaluating means.