Open Access

Axel Schaffland, Julius Schöning, Oliver Vornberger, Gunther Heideman

• Comparing two or more images taken on different dates from the same vantage point is beneficial for rescuers, researchers, and politicians to improve the assessment of natural disasters and climate change. Rephotography, i.e., shooting and comparing two or more images, can show fast changes in surroundings, e.g., before and after a tsunami, earthquake, and other environmental disasters, as well as slow changes like glacial movements. Retrieving these rephotographies is difficult since images from different shooting dates are usually not found on a single source, are without georeference, are lacking in metadata like precise recording times, and have different or no licensing information. Thus, rephotography is time intensive, costly, and not easy to use by rescuers. Overcoming the drawback and providing rephotography after disasters, our web portal re.photos addresses the difficulties of automatic image registration for large scene changes as happened after, e.g., earthquakes. Once the images are registered, georeferenced, and stored in a database, our web portal provides this in an easy-to-use interface. This database of compilations can be queried via metadata search. Rephotographies of two or more images is visualized as a table or on an interactive map. We provide custom interactive registration methods to register complex compilations with only a few fixed corresponding landmarks in the before and after images. By providing these interaction methods, rephotography for disaster management become valuable, e.g., by registering images of flooded or destroyed areas within minutes. re.photos allows its users to retrieve existing compilations, create template images that colleagues or citizen scientists can rephotograph, and register, georeference and persistently publish their rephotographic compilations.