Image Watermark

What a watermark does and how this tool builds one

A watermark is text laid over an image to assert ownership, deter casual copying, or brand a photo. This tool adds a text watermark entirely in your browser using the HTML <canvas> element. When you upload a picture, it is drawn onto a canvas, your watermark text is painted on top with the font, colour, opacity, and position you choose, and the combined result is exported as a PNG. Your original file is never uploaded — the FileReader API reads it locally, so nothing leaves your device.

One detail worth knowing: the on-screen preview is scaled down so it fits comfortably (the longest side is capped at 800 pixels), but when you click Download PNG the tool re-renders the watermark at your image's full original resolution. It scales the font size and padding by the ratio between full size and preview size, so a watermark that looks right in the preview comes out crisp and proportionally identical in the saved file.

The settings, and what each one really controls

• Opacity is the single most important choice. It ranges from 5% to 100%. Low opacity (around 30–50%) lets the image show through, which protects the photo while staying readable; full opacity is bold but can hide detail underneath.
• Font size is in pixels relative to the original image, not the screen. On a 4,000-pixel-wide photo a 36-pixel font is tiny; scale it up to a few hundred pixels for a watermark that survives cropping and resizing.
• Colour should contrast with the area it sits over. White reads well on dark or busy photos; a dark colour suits bright, light images.
• Position offers nine presets (the corners, edges, and centre) plus a Custom mode. The text is always drawn with a small padding from the edges so it never touches the border.

Dragging to an exact spot

The nine presets cover most needs, but when you choose Custom position you can click and drag the watermark directly on the preview canvas. The tool stores the position as a fraction of the image (for example, 0.5, 0.5 is dead centre), so when it re-renders at full resolution the watermark lands in the same relative place regardless of the original dimensions. Dragging only works in Custom mode; the presets snap to fixed anchors.

Repeat / tile mode for serious protection

A watermark in one corner is trivial to crop out. Toggle Repeat / tile and the tool stamps your text across the entire image in a diagonal grid, rotated 30 degrees, at an interval of five times the font size. This is the technique stock-photo libraries use: because the marks cover the whole frame, there is no clean region left to crop or clone away. The trade-off is that tiling is visually intrusive, so it suits proofs, comps, and previews you send to clients rather than a final deliverable.

A worked example

Imagine a 3,000 × 2,000 px photo you want to share as a low-commitment proof. Upload it; the preview shrinks to 800 × 533 px. Type © Studio North 2026, pick white, set opacity to about 0.4, and choose a font size that looks right in the preview — say 36 px. Enable Repeat. On screen you see a faint diagonal lattice of your text. When you download, the tool multiplies the 36 px font by the scale factor (3000 ÷ 800 ≈ 3.75), drawing the text at roughly 135 px on the full 3,000-pixel canvas, so the exported PNG carries the same lattice at full quality. The client can see the image clearly but cannot lift a clean copy.

Practical tips

• Match contrast to the busiest area, not the average. A white mark vanishes against a bright sky. If your image has both light and dark regions, the centre or a tiled pattern spreads the risk.
• Use opacity, not a faint colour. Lowering opacity keeps the text crisp while letting the photo through; choosing light grey instead can look muddy.
• Bigger is safer. A watermark that occupies a meaningful share of the frame is far harder to remove than a small corner tag.
• Output is always PNG. PNG is lossless, so the watermark edges stay sharp. If you need a smaller JPEG afterward, run the result through a separate compressor.
• Watermarks are not encryption. A determined editor can sometimes paint over a simple mark. Tiling and reasonable opacity raise the effort enough to stop casual reuse, which is the realistic goal.

Common use cases

Photographers send watermarked proofs before payment; designers stamp client comps so drafts are not mistaken for finals; sellers brand product shots to discourage competitors from reusing them; and anyone posting an image publicly can add a copyright line to make ownership clear. Because the whole process is local and instant, you can iterate on placement and opacity until it looks right without uploading anything.