Watermark Tool
Add a text watermark to your images in the browser — with an honest account of how much protection a watermark actually provides.
Upload an image to start.
The tiled watermark used to miss the corners of a long thin image
Tiling turns the canvas 30 degrees about the centre and then walks a grid outwards. The grid used the image's own width and height as its limits — but those limits are being applied inside a rotated frame, and once the canvas is turned the corners no longer sit within them.
| Shape | Needs | The loop reached | |
|---|---|---|---|
| Landscape 4:3 — 800×600 | ±496, ±460 | ±800, ±600 | covered |
| Portrait 3:4 — 600×800 | ±460, ±496 | ±600, ±800 | covered |
| Square — 1000×1000 | ±683, ±683 | ±1000, ±1000 | covered |
| Widescreen 16:9 — 1920×1080 | ±1101, ±948 | ±1920, ±1080 | covered |
| Tall banner 1:10 — 100×1000 | ±293, ±458 | ±100, ±1000 | gap |
| Wide banner 10:1 — 1000×100 | ±458, ±293 | ±1000, ±100 | gap |
| Very tall 1:5 — 400×2000 | ±673, ±966 | ±400, ±2000 | gap |
3 of the 7 shapes left a corner unstamped. On the worst of them the loop reached 34% of the span it needed, so two corners came out clean. A watermark with a gap in it is worse than no watermark, because it looks like it worked.
It went unnoticed because photographs are 4:3 and 16:9, and both have room to spare — a square needs only 0.68 of its side and the loop gave it 1.0. The shapes that failed are banners, screenshots of tall pages, and portrait phone captures, which is to say the ones people watermark when they are protecting something rather than decorating it.
The fix is one number: half the diagonal
Whatever the rotation, no point of a rectangle is further from its centre than half its diagonal. Use that in both directions and the covering is correct for any shape and any angle, with no trigonometry at the call site.
| Shape | Furthest corner | Half the diagonal | |
|---|---|---|---|
| Landscape 4:3 | 496 | 500 | covered |
| Portrait 3:4 | 496 | 500 | covered |
| Square | 683 | 707 | covered |
| Widescreen 16:9 | 1101 | 1101 | covered |
| Tall banner 1:10 | 458 | 502 | covered |
| Wide banner 10:1 | 458 | 502 | covered |
| Very tall 1:5 | 966 | 1020 | covered |
Checked at 6 rotations rather than just this one, because a bound that only works at 30 degrees is a coincidence rather than a fix. The tight case is a square turned 45 degrees, where half the diagonal is exactly what is needed and not a pixel more.
It stamps some tiles whose centres fall outside the picture, and those are simply clipped. On the squarer shapes it actually draws fewer tiles than before, because a circle of that radius is smaller than the old rectangle of side 2W by 2H.
How to use
- Choose your image and enter the watermark text.
- Set position, size and opacity.
- Place it over the subject if deterrence matters.
- Download the watermarked copy and keep your original.
Frequently asked questions
Does a watermark actually protect my image?
Only against casual reuse, and it is worth being clear about that. A watermark in a corner is trivially cropped, and one over the image is increasingly removable by software. What it does well is discourage lazy copying and carry attribution when an image spreads — neither of which is legal protection.
Where should I place it?
That is the real trade-off. A corner watermark preserves the image and gets cropped out; one across the subject survives but damages what you are showing. Photographers selling prints often use a large obtrusive one on previews precisely because the preview is not meant to be usable.
What actually protects an image legally?
Copyright, which you hold automatically on creation in most countries. Registration where it is available strengthens enforcement, and metadata recording authorship helps establish provenance. A watermark is evidence of intent rather than a legal mechanism.
Should I use a semi-transparent watermark?
Usually yes. Full opacity ruins the image and low opacity is easy to remove. Something around a quarter to a half is the common compromise, visible enough to deter and light enough to leave the picture usable — which is the balance most people actually want.
Does this modify my original file?
No. The watermarked version is produced as a new image for you to download, and the original on your device is untouched. Keeping an unwatermarked master is important, since the watermark cannot be cleanly removed from the output afterwards.
Does my image get uploaded?
No. Everything happens in your browser, so the picture never leaves your device — which is worth knowing given that many online watermarking services upload the very images you are trying to control.
🔒 This tool runs entirely in your browser. Nothing you enter is uploaded, logged, or stored.