The transparent-logo bug, and why this page mentions it
A logo is almost always a PNG with a transparent background. Stamp it onto a photo and the transparency must be preserved — the photo should show through the parts of the logo that are not ink.
A surprising number of watermark tools get this wrong. They draw the logo onto a white canvas somewhere in the pipeline, and what lands on your photo is the logo inside a white rectangle. It looks obviously broken and it is entirely avoidable.
This tool composites with the alpha channel intact, and the behaviour is checked by a test that stamps a logo with deliberately transparent corners onto a flat green picture and asserts those corners are still green.
A watermark is a deterrent, not a lock
A visible watermark makes casual reuse obvious and inconvenient. It does not make a picture uncopyable, and anyone determined enough will remove it — content-aware fill has been good at this for years.
So place it where removal costs something. A mark tucked in a corner crops off in seconds. A mark across the middle of the subject, at low opacity, cannot be removed without damaging the thing worth stealing.
Tiling is the strongest version of that trade: it covers the whole picture, so there is nowhere to crop to. It is also the most intrusive, which is the point — proof copies and contact sheets are exactly what it is for.
Opacity, size and the readable middle ground
Around 25–40% opacity is usually the sweet spot: clearly present, not so heavy that it ruins the photograph you are trying to show. Below about 15% it stops deterring anybody; above about 60% you may as well not send the picture.
Size matters as much as opacity. A large, faint mark is harder to remove and less visually intrusive than a small, opaque one — the eye reads the small dark block as damage and the large faint one as a texture.
Rotation helps for the same reason. A mark at 30 degrees crosses more of the subject and sits awkwardly against the picture's own lines, which makes it harder to patch out.
Nothing is uploaded
Both the photograph and your logo are processed entirely in your browser. This site makes no external requests at all, which you can confirm in your browser's network tab.
That is worth something specifically here: a logo file is often the highest-quality copy of a brand asset that exists outside a design system, and uploading it to a free tool to have it stamped onto a photo is a strange thing to do with it.
For a whole shoot, the bulk tool applies the same settings to up to fifty images and returns a ZIP.