Animals tend to use a combination of four tools to detect distance. Stereo vision, parallax, focus detection and scene context. Independent movement is not requ

Animals tend to use a combination of four tools to detect distance. Stereo vision, parallax, focus detection and scene context. Independent movement is not required for any of these (though it can help generate parallax.) Humans (and other animals) can learn to do pretty well with one eye and no head movement given the appropriate training regime. It makes the software problem harder but it certainly is possible.