A picture arrives from a source. It may be the story. You have to decide whether to publish, how to caption it, and how much of your own credibility to lend it — often before the end of the day.
This is a working order of checks, and an argument about one specific point: why the file itself should be the last thing you look at, and why it should not leave your machine while you look.
The problem with uploading
Most image-checking tools work by taking your file. You upload, their model looks at the pixels, you get a percentage back.
For a newsroom that is a real problem, and not a theoretical one:
- The file may identify the source. Camera serial numbers, GPS coordinates and timestamps are routinely embedded. Handing that to a third party is a disclosure you did not intend and cannot take back.
- You do not control retention. Whatever the terms of service say today, the file is on somebody else's disk.
- If the material is sensitive — abuse imagery, documents, anything involving a minor — uploading may be unlawful regardless of your intent.
The safe default is that nothing you have not published leaves your machine. That is achievable now for the metadata and provenance layer, which is where most of the decisive evidence lives anyway.
The order that works
1. Provenance, if there is any
Ask first whether the file declares its own origin. A signed Content Credentials manifest is the strongest thing you will ever get: a cryptographic record of what produced the image and what was done to it, which cannot be edited without breaking the signature.
Adoption has moved fast. Most of the major wire services and public broadcasters now sign what they publish, and several camera manufacturers sign at capture. If your file carries a valid signature that binds to those exact bytes, most of your questions are answered in one step.
Two cautions that matter more than they sound:
A signature is not a verdict on the picture. It proves the record is intact and belongs to this file. It does not prove the person named is who they say — that needs the certificate checked against a recognised trust list, which is a separate step.
"Signed" is not the same as "signed for this image." A manifest can be lifted off a genuinely signed photograph and attached to a different one. The signature stays perfectly valid; what breaks is the binding between the manifest and the pixels. Any tool worth using checks that binding and says so separately. If it only tells you a signature is present, it has not told you anything.
2. Reverse image search
Before analysing anything, find out whether the image already exists. Google Images, TinEye and Yandex each have different indexes and different strengths — Yandex is markedly better on faces and interiors, TinEye on finding the earliest instance.
This catches recycled photographs, which remain far more common than generated ones. It also frequently dates the image, which is often the whole story: a genuine photograph presented as something that happened yesterday.
3. What is in the picture
Geolocation and chronolocation are still the strongest verification methods available and they do not involve the file at all. Shadow direction and length against the claimed date. Signage, licence plates, architecture, vegetation. Cross-referencing satellite imagery.
None of this can be faked away by a better model, because it is checked against the world rather than against the file.
4. The file itself, last
Now open it. Camera body, lens, exposure, timestamp, GPS. Generator settings if it was made by a model — image generators write the prompt, the model name and the seed into the file, and almost nobody removes them.
Two things to hold onto:
EXIF is plain text. It can be copied from a genuine photograph onto a fabricated one. Camera metadata is supporting evidence, never proof.
Most files have nothing left. Anything that passed through a social platform or a messenger has been re-encoded and stripped. That is not a tool failing — the information is gone. Ask the source to resend "as a file" or "as a document" rather than as a photo. It is the single highest-yield request in this entire process, and it costs one message.
Writing it up
The verification is only half the job. The other half is describing what you found without implying more than you have.
Do not print a percentage. A confidence number invites the reader to treat it as a measurement. The same detector that scores in the nineties on an easy test set drops towards a coin flip against images built to look authentic, and the number looks identical in both cases.
Say which layer you checked. "The file carries a signed record from AFP that matches the image byte for byte" is a different claim from "the file's structure is consistent with AI generation", which is different again from "the metadata was stripped and we could not establish anything." Readers can follow that distinction if you make it.
Publish the absence. "We could not verify this image" is a finding, and it is the most common one. Treating silence as innocence is the single most frequent error in coverage of manipulated media.
Keep the original. Archive the file as received, not a screenshot of it. A screenshot destroys everything you would need to re-examine later, including the timestamps.
Where SynthCheck fits
SynthCheck covers step one and step four, in the browser, without the file leaving the machine. It reads the provenance layer and verifies C2PA signatures locally — including whether the signature actually binds to these bytes — and it reads generator metadata and the structural fingerprints that survive metadata stripping.
It does not do steps two and three, and it does not look at pixels. It has no classifier and will not produce a number. When it cannot establish anything it says so, which on material saved off social media is often.
It is open source, so the claim that nothing is uploaded can be checked rather than believed — including by your own security people, who are right to ask.
The short version
Provenance first, reverse search second, the world in the picture third, the file last. Ask for the original as a document. Never upload anything you have not already published. And when you write it up, describe the layer you checked rather than the confidence you feel.
Check a file now — nothing is uploaded, everything is read on your own device.