1. A navigation system for a vehicle, the system comprising: at least one image capture device configured to acquire a plurality of images of an environment of a vehicle; a radar sensor to detect an object in the environment of the vehicle and to provide and output including range information indicative of at least one of a range or range rate between the vehicle and the object; and at least one processing device programmed to: receive the plurality of images from the at least one image capture device; receive the output from the radar sensor; determine, for each of a plurality of image segments in a first image, from among the plurality of images, and corresponding image segments in a second image, from among the plurality of images, an indicator of optical flow; determine a value indicative of an expected optical inflation associated with the object in the plurality of images based at least upon the range information from the output of the radar sensor; determine one or more areas of the second image where the value indicative of an expected optical inflation associated with the object substantially matches the indicator of optical flow; identify a target object region, including at least a subset of the determined one or more areas of the second image; and cause a system response based on the identified target object region.