While I am definitely into photography, I only recently learned about rephotography -- the practice of returning to the site of a previous photograph and taking a new image, then comparing them. Third View is a "rephotographic survey of the American West," showcasing series of rephotographs (a minimum of two, but often three) from a variety of locations. From the site:
Third View revisits the sites of historic western American landscape photographs. The project makes new photographs, keeps a field diary of its travels, and collects materials useful in interpreting the scenes, change and the passage of time. The Third View project began in 1997 and completed fieldwork in the year 2000. Over the course of four years the project revisited 109 historic landscape sites, all subjects of nineteenth-century American western survey photographs. The project's "rephotographs" were made from the originals' vantage points with as much precision as possible. Every attempt was also made to duplicate the original photographs' lighting conditions, both in time of day and year.
Third View photos will be on display at the Blue Sky Gallery in Portland through September. There's more about rephotography at Wikipedia, including a description of the Second View project (a precursor to Third View, above). Be sure to check out the External Links section at the bottom of the page, where I found a new personal favorite: In Twin Peaks, a project to rephotograph filming locations from the series.