How Do AI Image Detectors Work?

Updated July 1, 2026 · 7 min read

You upload a photo, and a few seconds later you get back something like "87% AI-generated." What's actually happening under the hood? Here's a plain-English look at how AI image detectors work — and why some are far more reliable than others.

Fastest check: a detector is a machine-learning model trained on millions of real and AI images; it spots artifacts invisible to the eye and returns a probability. Try one on any image.

Try it below →

The problem they solve

Modern generators — Midjourney, DALL·E, Stable Diffusion, Flux — produce images with few visible tells. The human eye simply isn't reliable anymore (see how to tell if an image is AI-generated). Detectors step in where our eyes give out.

It's a trained classifier, not a rulebook

An AI image detector doesn't follow a checklist of "look for bad hands." It's a machine-learning model shown millions of labeled examples — real photographs and AI-generated images — until it learns, on its own, the patterns that separate the two.

What it actually "sees": statistical fingerprints

Every generator leaves behind subtle, consistent traces — in the frequency spectrum, pixel-level statistics, texture, and how detail is distributed. These "fingerprints" are invisible to us but measurable to a model. Detectors also pick up on irregularities in reflections, skin texture, and background detail.

From image to probability

Under the hood, the image passes through a neural network (a CNN, a vision transformer, or a CLIP-style encoder) that turns it into a compact numeric representation. A classifier on top converts that into a single number: the probability the image is AI-generated — e.g. "92% AI." It's a confidence score, not a yes/no verdict.

The thing that decides accuracy: training-data diversity

Here's the part most people miss. A detector can only recognize the kinds of generators it was trained on. Train it on a narrow slice, and it looks brilliant in tests but misses images from a generator it's never seen — sometimes catching only a few percent of them. Train it on a diverse mix of generators, and it generalizes far better to new ones. Breadth of training data, not clever tricks, is what separates a detector that works in the real world from one that only works in the lab.

The limits worth knowing

No detector is perfect:

  • Results are probabilities, so false positives and false negatives happen
  • Brand-new generators, heavy compression, or heavy editing can throw it off
  • Non-photographic images (screenshots, digital art) can confuse detectors not trained to expect them

Use the score as a strong signal alongside metadata and provenance checks — not as absolute proof.

Watermarks are a separate check. Google hides one called SynthID in content its AI makes, and only Google's tools can read it: see how to check an image for SynthID, and why a missing watermark proves nothing on its own.

Curious how well you do without a detector? The AI or real quiz pairs real photos with AI images of the same thing.

See a detector in action

Upload any image below and watch it return an AI-or-real probability in seconds. Free, no sign-up, and your image is deleted after analysis.

⬆️

Drag & drop, paste, or click to upload

PNG · JPG · WEBP · HEIC — your image is analyzed privately and deleted

No image? Try one:

Frequently asked questions

Are AI image detectors accurate?

The best are highly accurate on generators they've been trained on, but they work in probabilities, not absolutes. Treat the score as a strong signal and combine it with visual and metadata checks.

Can AI image detectors be fooled?

Yes — a brand-new generator, heavy compression, or aggressive editing can reduce accuracy. Detectors trained on a diverse mix of generators are much harder to fool than narrowly-trained ones.

Do detectors work on any AI generator?

Only as well as their training covers it. A detector trained on many generators generalizes to unseen ones far better than one trained on just a few.