画像透かし

A watermark tool that stamps custom text over your image, with control over the size, color, opacity and one of nine positions, all shown in a live preview as you adjust them.

Watermarks have a few everyday jobs: discouraging casual reuse of a photo, branding an image with your name or site, or marking a picture as a draft, sample or confidential before you share it.

Because the watermark is drawn on your device, your image never leaves it, and nothing is uploaded to a server.

Everything is drawn in your browser with the Canvas API, so it is quick and the preview updates live as you tweak the settings.

The size is set as a percentage of the image width, so the watermark scales sensibly whether the picture is a small thumbnail or a large photo, and looks consistent across different images.

Opacity lets you choose between a bold stamp and a subtle, semi-transparent mark that protects the image without hiding what is underneath, while the nine-position grid places it exactly where you want, from a corner to the center.

It is worth being realistic: a visible watermark deters casual copying but is not theft-proof, since a determined person can crop or edit it out. It raises the effort, which is enough for most everyday sharing.