Google's SynthID Detector Is Now Free for Everyone. What That Means If You Make Images With AI
There is a mark inside the images Google's AI tools make, and inside images made through ChatGPT since May. You cannot see it. It does not change a single color you would notice. It is designed to survive cropping, filters and compression. Until this week, reading it took either an early-access invitation for media professionals or the right question typed into Gemini.
On October 7 that changed. Google opened its SynthID Detector to everyone, at synthid.com, so that anyone can check "if an image, video, or audio file was made with AI from Google or our partners." The partners it names are OpenAI, NVIDIA and Kakao, with Apple "coming soon."
If you make things with AI and hand them to anyone else, this is the most important tool launch of the week, and it is not a tool for making anything. It is a tool for checking. The people who will use it most are your clients, your editors, contest judges and the stranger in the comments.
My position is simple. Telling people how you made something is now cheaper than being caught. And at the same time, the checker is much less useful than it looks, because a clean result tells you almost nothing.
A microscope video shows how this plays out
The clearest example arrived before the public launch.
In September, Nikon named the winner of its Small World in Motion competition, a video of airway cilia filmed through a microscope. Nikon's rules say plainly that "AI-generated videos are not permitted." Then an MD/PhD student at UT Southwestern Medical Center ran the video through Gemini and, as PetaPixel reported, got back a hidden SynthID result. He raised it in the comments on Nikon's LinkedIn post, according to CNN. Microscopists piled in with other problems: structures that "pop in and out of existence," cilia that "do not match the known size."
The entrant said he had used AI only after filming, to color similar-looking structures in his grayscale footage. Scientists replied that releasing the raw grayscale video would settle it. By October 1 Nikon said it was re-reviewing the entry, and on October 9 PetaPixel's headline reported a disqualification.
Look at who found it. Not the judging panel. A commenter with a free tool. And look at what would have helped the entrant most: a sentence, up front, saying exactly where AI touched the work, plus the raw files to back it up.
That is the new normal. With the detector public, any viewer can run the same check in a couple of minutes.
What the watermark is, in plain terms
A watermark you can see is a logo in the corner. You can crop it out.
SynthID works differently. When a Google model makes a picture, it nudges the pixel values in a pattern that carries a signal, the way a faint pencil mark in a printed page might carry a serial number. Your eye reads the picture. The detector reads the pattern. Google says the mark is "designed to stand up to modifications like cropping, adding filters, changing frame rates, or lossy compression," and that the audio mark "can't be altered by common modifications like adding noise, MP3 compression, or changing the speed of the track," per the SynthID page.
This is different from Content Credentials (the C2PA standard), which is a label attached to the file, a bit like a receipt stapled to a photo. A label can be stripped by re-saving or screenshotting. The watermark lives in the picture itself.
Who puts the mark in matters, so here is the current list as the companies describe it:
- Google: its image, video and audio models.
- OpenAI: images made through ChatGPT, Codex or the OpenAI API since May, and supported audio since a July update, according to OpenAI's provenance post. That post does not say SynthID covers Sora video.
- NVIDIA and Kakao: named as partners in Google's announcement.
So the realistic reading of a "yes" from the detector: some part of this file passed through a tool from one of those companies.
What the detector tells you, and what it does not
Google's own post does not describe limits. Reporting from Android Headlines and a summary of Ars Technica's coverage fills in the rest, so treat these as reported rather than confirmed:
- You sign in with a Google, OpenAI or Apple account.
- You get roughly ten checks a day across images, video and audio. Android Headlines reports the sign-in and the daily cap are meant to deter people trying to build watermark removers.
- The answer is a yes or no. The public version does not highlight which regions carry the mark, which Google's earlier internal tool did.
That yes-or-no is the whole problem with reading too much into it.
A "yes" is strong evidence that a partner tool was involved. It does not say how much. A frame made entirely by Gemini and a photo where you used a Google tool to recolor one corner can both come back marked. The microscope entrant's whole defense rested on that difference, and the detector cannot draw it.
A "no" is weak evidence of anything. Open models you run at home, like Qwen's image models or the MiniMax video models, carry no SynthID at all. Neither do tools from companies outside the partner list. The checker only reports on partner watermarks, so anything else simply does not register. A fully AI-generated image from an open model on your own computer will pass this check every time.
So the detector rewards honesty on the big closed tools and says nothing about the open ones. That is not a flaw you can fix by being clever. It is the shape of the tool.
Put this into practice
None of this needs a new budget. It needs four habits.
1. Check what comes in. Before you build a composite on a stock frame, a client-supplied background or a "photo" from a collaborator, run it through synthid.com. If it comes back marked and the client told you it was a real photograph, you want to know that before your name is on the finished piece, not after.
2. Check what goes out. Run your own deliverable through the detector before you send it. You probably know the answer. The point is to see exactly what your client, editor or contest will see, and to have the conversation on your terms. With roughly ten checks a day, save them for final files and anything you did not make yourself.
3. Write the disclosure line before anyone asks. One plain sentence in the delivery note or the entry form: "Background extended with Google's image tools; subject photographed on set." Or: "Color separation done with an AI model on the recorded grayscale data; raw files available." The Nikon entrant ended up explaining himself in LinkedIn comments. A sentence written first reads as professionalism. The same sentence written after a stranger posts a screenshot reads as a confession.
4. Keep your raw files. The microscope argument came down to one request: release the original grayscale footage. For photographers that means the RAW files. For illustrators, the layered working file. For editors, the original camera media. If you used AI for one step, your process files are what prove it was only one step. A detector cannot see your process. Your folder can.
And one habit to drop: never send a clean detector result as proof that something is human-made. You now know why it is not.
The honest limits
Here is what the tool will not do for you, said plainly.
It only reads one family of watermarks. Google, plus OpenAI images and audio, plus NVIDIA and Kakao. Everything else reads as clean.
It cannot measure how much AI was used. One AI-recolored corner and a fully generated scene can both read "yes." If your work mixes camera and AI, expect to explain, every time.
The details are thin. Google published no accuracy figures, and no false-positive rate, in its announcement. The quota and the sign-in rules come from press reports, not from Google's post.
It is English-only for now. Google says the tool is "available globally in English."
Ten checks a day is not a workflow for a busy studio. It is enough for a freelancer checking finals. It is not enough to screen a whole stock library.
Where this leaves you
For most of the past two years, the unspoken question behind AI-assisted work was "can anyone tell?" As of this week, for anything that touched Google's or OpenAI's tools, the answer is yes, anyone, for free, in a couple of minutes.
That does not mean you should stop using those tools. It means the question has changed to "did you say so?" The people who will come through this period with their reputations intact are the ones who disclose first, keep their process files and refuse to oversell a clean result.
So this week, take one finished piece you are proud of and run it through synthid.com. Then write the one-sentence disclosure you would want attached to it. If writing that sentence makes you uncomfortable, that is worth knowing now, while you still get to choose the wording.
Medium metadata
Title: Google's SynthID Detector Is Now Free for Everyone. What That Means If You Make Images With AI
Subtitle: Anyone can now check whether an image, video or audio file carries Google's or OpenAI's invisible AI watermark. Here is what a "yes" proves, why a "no" proves almost nothing, and four habits that protect working creatives.
Tags: Artificial Intelligence, Photography, Generative AI, Creativity, Ethics
Estimated read time: 8 minutes