How a QR code hides inside an image
Why a camera sees a code that people barely notice, which pictures work best and how to check the result before printing.
How it works
A scanner does not see colour — it looks for differences in brightness between neighbouring modules. So instead of pasting a black-and-white code over the photo, we take the brightness under each module and shift it slightly darker or lighter. Hue and saturation stay the same: red stays red, sky stays sky, and the pattern reads as the image’s texture.
Every variant is checked by a decoder against a phone-camera model — with blur, noise and uneven exposure, at the resolution of the final file. Auto-tuning keeps the weakest strength at which the code still scans reliably, so the visibility is minimal by design rather than by chance.
Which parts of a picture work
| Area | How the code hides | Tip |
|---|---|---|
| Even mid-tone background: sky, wall, fabric | Best | Place the code here first |
| Fine texture: leaves, sand, concrete | Well — modules get lost in the pattern | Raise the strength a little |
| Near-white or near-black area | More visible — there is no room for contrast | Move the code towards mid-tones |
| Face, lettering, logo | Poorly — the code fights the picture’s meaning | Keep clear of key details |
Size and placement
- Make the code small — a fraction of the frame: the picture keeps its meaning and the code becomes a detail worth finding.
- Minimum size is about 2.5–3 cm in print and 150–200 pixels on screen. Any smaller and the camera cannot tell the modules apart.
- Drag the square with a mouse or a finger: tuning updates instantly, so you can see where the code hides best.
- A short link means fewer modules — each one is larger and the code is easier to hide.
The three corner squares — the finder patterns — always stand out more than the rest: without them a phone cannot locate the code. Place the code so the markers land on parts of the picture where a square shape does not catch the eye.
Where to use it
- Posters and banners with an easter egg people want to scan.
- Covers, posts and stories where a regular code would spoil the composition.
- Packaging and labels with a busy design.
- Invitations, greeting cards and gift certificates.
- Shop windows, stands and menus where the code must be present but not shout.
How to test before printing
- Point the built-in camera of an iPhone and an Android phone at the screen from 30–50 cm.
- Print a proof on the same paper: matte and gloss give different contrast.
- Check under normal room light, not only by a window.
- If the code does not read on the first try, switch to Reliable or raise the strength.
The picture is processed in your browser and never uploaded. Download PNG for publishing: JPG compression eats the subtle brightness difference, so test a JPG file with a camera once more.