1. An image assessment device assessing an image pair used for three-dimensional measurement from plural captured images comprising: processing circuitry that: selects a first captured image from the plural captured images; acquires an imaging position and imaging orientation of the selected first captured image; acquires an object distance to be measured from a first imaging position that is the imaging position for the first captured image to an object to be measured in the first captured image; calculates an object position to be measured which is a position on an optical axis in capturing the first captured image and is at the object distance to be measured in a three-dimensional space from the first imaging position; selects a second captured image from the plural captured images; acquires a second imaging position that is an imaging position, imaging orientation, and angle of view for the selected second captured image; calculates an imaging range corresponding to the second captured image on the basis of the imaging position, imaging orientation, and angle of view for the acquired second captured image; and determines whether or not the calculated object position to be measured is within the calculated imaging range, and assesses that the first captured image and the second captured image are of the image pair if determining that the calculated object position to be measured is within the calculated imaging range, wherein the object position to be measured is calculated on the basis of the first captured image and not on the basis of the second captured image, wherein the imaging range is calculated on the basis of the second captured image and not on the basis of the first captured image, and wherein the processing circuitry assesses that the first captured image and the second captured image are of the image pair, further in a case a distance between the object position to be measured and the optical axis of a capturing device at the imaging position for the second captured image is equal to or less than a threshold.