1. A separation filter selection device comprising: an image input unit for inputting a captured image of a tire surface, the image including a characteristic portion; a memory unit for storing a plurality of filters for performing image processing of the captured image, storing a predetermined training image that corresponds to an image in which the characteristic portion has been separated from the captured image and that corresponds to an image resulting from image processing of the captured image using the plurality of filters, and storing a weighted image in which a weighting is set to a predetermined region of the captured image; a setting unit for setting as a separation filter a filter group combining two or more filters from the plurality of filters stored in the memory unit; an evaluation unit for performing image processing of the captured image with each of the two or more filters of the separation filter, and calculating an evaluation value of the separation filter on the basis of an image that is a differential image between a processed image after image processing and the training image and to which a weighting based on the weighted image is applied; and a separation filter selection unit for repeating the setting of the setting unit and the evaluation value calculation of the evaluation unit until the evaluation value is within a predetermined specific range, and selecting a separation filter corresponding to the evaluation value resulting from the repeated calculation as a separation filter for separating the characteristic portion from the captured image.