I was thinking about putting an automated license plate logger near my mail box to track in-and-out movement of vehicles. It would have timestamps and license plate numbers. I just thought it'd be interesting to see what patterns emerge, and, you never know, having a log like this could prove valuable in certain circumstances. Just wondering, however, if what I'm thinking about doing is legal. These data wouldn't be published.
You can basically take pictures of anything from your property if it is "public" (i.e. easily visible from your property). People on the road are in public, and have no reasonable expectation of privacy. The basic restrictions on photography are (1) you cannot trespass (you aren't), and (2) you cannot take pictures of certain government operations (e.g. airport border crossing – certain aspects of government prohibition may require lawsuit to rein in government policy that is at odds with the 1st Amendment; also secret military installations, for which there is specific law, 18 USC 795). Commercial exploitation of people who you photograph is strongly protected in California, and that is it.