1. An image processing device, comprising: a display having an image display area for displaying an image; an operation interface configured to designate an area in the image display area in a movable manner; and a filter processor configured to perform filter processing on the image within the area designated in the movable manner by the operation interface, wherein when an operation is performed by the operation interface in an intersectional direction with respect to the direction in which the operation of designating the area is performed in the image, the filter processor performs the filter processing to increase the filter effect applied to the image when the operation by the operation interface is performed in a first direction with respect to the intersectional direction, and to decrease the filter effect applied to the image when the operation by the operation interface is performed in a second direction with respect to the intersectional direction.