Webcam geo-localization using aggregate light levels

We consider the problem of geo-locating static cameras from long-term time-lapse imagery. This problem has received significant attention recently, with most methods making strong assumptions on the geometric structure of the scene. We explore a simple, robust cue that relates overall image intensity to the zenith angle of the sun (which need not be visible). We characterize the accuracy of geolocation based on this cue as a function of different models of the zenith-intensity relationship and the amount of imagery available. We evaluate our algorithm on a dataset of more than 60 million images captured from outdoor webcams located around the globe. We find that using our algorithm with images sampled every 30 minutes, yields localization errors of less than 100km for the majority of cameras.