1. An image-augmented inertial navigation system comprising: an inertial navigation system configured to estimate a navigation state vector; an imager configured to output pixel signals associated with terrain features passing through a field view of the imager over a plurality of image frames; and a processing unit operatively connected to the inertial navigation system and the imager, the processing unit being configured to sense a distance from the imager to a centroid of one or more of the terrain features passing through the field of view of the imager for a given image frame based on the pixel signals, track each terrain feature from a first image frame containing the terrain feature to any subsequent image frame while the terrain features remain within the field of view of the imager, calculate NED coordinates position information of the inertial navigation system relative to first tagged coordinates of each tracked terrain feature, and update the navigation state vector of the inertial navigation system based on the calculated inertial navigation system position information.