In the introduction to Interpreting Long-Term Trends in Blue Mountain Ecosystems from Repeat Photography, Jon Skovlin and Jack Ward Thomas define repeat photography as, “the art of finding the site of a previous photograph, reoccupying the original camera position, and making a repeat photograph of the same scene.”
This method of taking photographs of a specific location at two or more different times is a powerful visual resource for scientific study and education in the domain of forest and land management. It can be used to document the effects of natural events and processes on landscape systems such as ecosystem succession, fires, regeneration and climate change. Repeat photography is also useful as sociological evidence of transitions in human environments, displaying land use change, urban development and demographic variation.
Practitioners of repeat photography may revisit their own original photos, or they may attempt to recreate photographs taken by others, the origins of which can sometimes be poorly documented or unknown. The precision of repeat photography sets can vary depending on whether the photographer takes pains to capture the subject from the exact same location (or "camera point"), time of year, camera angle and with similar weather conditions as were present in earlier photos. In cases where earlier photographs lack precise documentation it becomes necessary for the individual creating a repeat photo to conduct historical research.
“Before and after” photography has been popular since the onset of photographic technology and was adopted early on by scientific researchers such as glaciologists, ecologists and geologists, as well as the artistic and cultural heritage community. The first documented instance of technical repeat photography is the work of Bavarian mathematician and surveyor Sebastian Finsterwalder in 1888, which is housed at the U.S. Geological Survey in Tucson, Arizona. Methods have not changed significantly since repeat photography was originally conceived, but digital technologies such as Geographical Information Systems (GIS) and application software such as Google Earth have made a significant impact in the ability to precisely determine previously unknown locations of photos and photo sets and link related items from varying sources and across collections.