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 an evaluation unit configured to calculate one or more of an evaluation value of a likelihood of being a line-like structure and 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 evaluation unit.