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Who's Time Is It Anyway?: Investigating the Accuracy of Camera Timestamps

People take photos all over the world at all times of day; each photo depicting a place and a moment worth capturing. In the context of multimedia analysis and social computing, accurate location and time information about where and when these photos were taken is of importance for understanding event semantics, image content and many other purposes. While location information associated with photos is known to be relatively accurate, time is not. From a sample of 10 million public Flickr photos, we observe that 37% of the photos differ more than an hour between their camera timestamps and GPS timestamps with respect to local time at the locations where the photos were taken. Erroneous time information may adversely influence the correctness of any kind of temporal analysis that relies on camera timestamps, as well as research and real-world applications that require accurate knowledge of when and where photos were captured. In light of our observations we propose a simple yet effective metadata-only technique for improving the accuracy of camera timestamps.