Your caption examples are what made me think of the photo metadata, other content/context you could include in the photo. However, the user's own captions are p

Your caption examples are what made me think of the photo metadata, other content/context you could include in the photo. However, the user's own captions are probably more meaningful (and easier to implement ;). Photo metadata might be low quality or wrong if the image happens to get transcoded somewhere in the pipeline from camera to MMS to mobile carrier network to your service.