How do you know that a photo accurately represents what the camera captured?

The widespread availability of digital image editing and AI image generation has made this a difficult question for photojournalists, publications, and the people who view their work. It has so far been tackled by standards like C2PA, which is designed to to help verify an image’s authenticity, as well as watermarks like Google’s SynthID, which can be used to detect AI generated images. Now, Apple is taking a swing at the problem with a system it calls Apple Reference Image.

Apple Reference Image is an optional camera mode that captures a cryptographically signed copy of raw sensor data from the phone’s main camera. Apple’s Private Cloud Compute can later develop that data into a “reference image” it stores so people can check if the picture was altered after it was captured.

“Generative AI has changed the nature of what you can and can’t do with manipulating visual imagery, and how easy it is to do it,” says Hany Farid, a professor at Dartmouth who has worked on image forensics for nearly 25 years. “I find it interesting when one of the world’s most valuable companies get into this space. When a company like Apple gets in the game, it’s getting serious.”

How Reference Image works

Apple Reference Image is only available on the iPhone 18 Pro and Pro Max, and will only function with the 48MP main camera. This limited debut, which excludes the new folding iPhone Duo, is due to Reference Image’s security requirements. The sensors which support Reference Image are initialized at the factory to generate secure keys before they ship, which means Reference Image only works with those specific sensors.

Switching the iPhone 18 Pro’s camera to Reference mode reboots the sensor into this secure environment, after which Reference Mode captures photos as raw sensor data. It’s bundled with metadata and signed with the sensor’s private key.

Importantly, all these steps occur before data leaves the sensor. This is why the sensor is set up with a secure key from the factory, and also why no image processing occurs. “All the bits are coming off that sensor before anything happens,” Farid says. “And only Apple can do that on an Apple device, because they’re doing it on hardware, not software.”

However, this also means the image is not viewable the moment it comes off the sensor. To make it viewable, it must be sent to Apple’s Private Cloud Compute servers. The server checks the validity of the secure key and uses AI analysis to determine if the sensor data falls within expected parameters for an image captured by the iPhone 18 Pro camera. If everything checks out, the server executes image processing, re-signs the image, and sends it back to the user.

Why not just use C2PA?

Apple isn’t the first company to take a stab at validating the authenticity of images taken by a camera. The most prominent example is the Coalition for Content Provenance and Authenticity (C2PA) standard, released in January of 2022 and backed by a consortium that includes Adobe, Microsoft, the BBC, and most major camera companies. Leica released the first camera with C2PA support in 2023, and many devicemakers have since adopted the standard, including Google for its Pixel smartphones.

Sam Gregory, former executive director of human rights organization WITNESS and advocate for photo authenticity, says Apple’s decision to create an alternative to C2PA seems rooted in concerns about the standard’s vulnerabilities.

“Apple Reference Image is potentially providing a fix to a critical element in C2PA: how do you, as conclusively as possible, prove that the initial image from a camera is reliable and untampered with?” says Gregory. C2PA has suffered several security incidents to date including a vulnerability that forced Nikon to revoke all C2PA certifications and a recently revealed exploit that circumvents Google’s Pixel C2PA implementation. “If you can’t trust that the initial image is real, all other elements are building on shaky foundations,” Gregory says.

Reference Image also addresses C2PA’s privacy issues. A report released by WITNESS on July 8 presented seven scenarios in which C2PA can expose details about journalists who capture or edit a photo. While there are ways to prevent these issues, they require users to have a high level of understanding about how the standard works.

Apple says its PCC servers, which were developed originally to handle Apple Intelligence, can authenticate a Reference Image without exposing details of the device which captured it to any entity, including Apple. This requires users to trust that Apple’s infrastructure works as advertised, though the company releases third-party audits of PCC’s infrastructure on a quarterly basis. The PCC infrastructure also gives Apple the option to revoke the authenticity of images or sensors that are believed to be compromised.

A new option, but not a perfect solution

The hardware and infrastructure Apple has built to support Reference Image addresses criticisms of C2PA, but the company’s tight control over Reference Image creates its own problems. Gregory says Apple’s work on securing the sensor is useful but that the “closed implementation is a control choice, not a technical necessity.”

That control extends to how images are viewed. At launch, Apple Reference Images were only viewable on iOS, iPadOS, and macOS devices, and only in Apple’s own apps. A third-party API for viewing the photos in third-party apps on Apple platforms is available though, due to its recent release (iOS 18 will launch on September 18) no third-party apps support the feature at launch.

Gregory worries this could create a situation where images outside the Reference Image ecosystem are viewed as less credible than those inside it. “We already see the absence of credentialing on an image get used against people in critical documentation and journalism,” he says. “This ratchet effect, where technology raises the bar of expectations for those least able to clear it, will impact people who don’t have access to or use Apple devices.”

Farid also acknowledged the limitations to the company’s approach, but he’s optimistic that its debut will make more people think about the need to authenticate images, as well as other media, such as video and audio (which Apple Reference Image does not address). “I don’t think they solve the problem. It’s not like we can all pack it up and go home now,” he says. “But my overriding thought is that this is cool. I hope that other major tech companies will look at this and say, ‘Hey, maybe we need to get involved in image authenticity and verification.’”