iPhone metadata includes several fingerprints that can be used to differentiate between different devices, including a serial number, uptime in seconds, and shu

iPhone metadata includes several fingerprints that can be used to differentiate between different devices, including a serial number, uptime in seconds, and shutter release count (depending on the model of iPhone you have). (source: me examining as many different iPhone models and instances to build deduping heuristics for PhotoStructure)