1. An image processing device comprising: an evaluation value calculation section that calculates an evaluation value that is used to determine whether or not an inter-frame state of an object within a captured image is a stationary state; an estimated noise amount acquisition section that acquires an estimated noise amount of the captured image; a determination section that determines whether or not the inter-frame state of the object is the stationary state based on the evaluation value, the estimated noise amount, and a specific condition; and a noise reduction processing section that performs a first noise reduction process that is a time-direction noise reduction process on the captured image when it has been determined that the inter-frame state of the object is the stationary state, and performs a second noise reduction process that includes at least a spatial-direction noise reduction process on the captured image when it has been determined that the inter-frame state of the object is not the stationary state, the specific condition being an observation state of the object, or whether a target area of a noise reduction process belongs to a front-field-of-view area or a side-field-of-view area, or a type of the captured image.