New details have emerged about how Apple's Reference Image mode, available on the iPhone 18 Pro and Pro Max, works to authenticate photographs against manipulation. The feature works by embedding a cryptographic signature directly within the camera sensor at the moment of capture, using a unique private key generated during manufacturing, so any later alteration of the image data causes it to fail verification. Apple's Private Cloud Compute service then checks this record and issues a further digital signature, giving users a way to prove a photo is genuine as AI-generated and doctored images become harder to spot by eye.

The feature is opt-in and must be switched on via Settings > Camera > Reference Image before use, after which it can be selected as a mode within the camera app. Captured evidence is stored in the RAW "digital negative" (DNG) format alongside the finished photo, and can be kept indefinitely or shared for later development; once developed, the negative is moved to deleted photos and erased automatically after 30 days unless recovered. The system also records a signed timestamp window, independent of the phone's own clock, to verify when a photo was actually taken, and continues working offline using the last timestamp received before syncing again once reconnected.