rePhoto, available for iOS and Android devices, is an image capture application explicitly designed to support repeat photography -- the process of taking a new image from exactly the same perspective as a previous image. In rePhoto this is made easier by showing the previous picture half see-through so that a new picture can be more accurately aligned.
The app shows a map (centered on current phone location) with nearby rePhoto subjects. The user can select a subject, takes an aligned picture, and that image, along with all meta-data supported by the phone (GPS, time stamp, exposure, tilt, roll, temperature (if available), etc...) are uploaded to the rePhoto database, and made available on this website.
Not all changes are important scientific measurements! rePhoto lets use your smart phone to take a new picture (with front or back cameras) aligned to any photo in your photo library, including images taken by other cameras.
The app helps you align the new picture, showing the old picture half see-through, or just on the left (or top or right or bottom) half of the screen, or with a variety of vertical and horizontal blinds effects. When you take the picture it is saved only to your phone (not uploaded to any database), both in its original form and with the overlay.