Overview
Introduction
This tool overlays a semi-transparent text watermark onto a JPG, entirely client-side, either as a single centered mark or repeated in a tiled grid across the whole photo.
It's built for the common 'proof' or 'sample' watermark use case: visible enough to deter casual reuse of an unlicensed image, without a server round-trip.
What Is JPG Watermarker?
A client-side JPG watermarking tool that alpha-blends the built-in bitmap font's glyph pixels into the existing image at a chosen opacity, rather than overwriting pixels outright the way a solid text stamp would.
Two layouts are supported: a single centered watermark, or a tiled repeating pattern sized to the text so it covers the entire image evenly.
How JPG Watermarker Works
For each 'on' pixel in the bitmap font's glyphs, the tool computes a linear blend between the existing pixel color and the watermark color, weighted by the chosen opacity (0 = invisible, 1 = fully opaque); this is standard alpha compositing applied per-glyph-pixel rather than to the whole image.
In tiled mode, the tool computes one text block's rendered width and height (plus a small gap), then repeats that same blend operation at every grid position across the canvas.
When To Use JPG Watermarker
Use it before sharing preview/proof images publicly, to visibly mark ownership on portfolio samples, or to discourage casual reuse of photos shared for feedback.
The tiled layout is best for full-image protection; the single centered layout is less intrusive and better suited to a subtle brand mark.
Often used alongside JPG Text Adder, JPG Annotator and PNG Watermark Adder.
Features
Advantages
- Runs entirely client-side.
- Tiled layout provides watermark coverage even if the image is later cropped.
- Opacity, scale, and color are all independently adjustable.
Limitations
- Text-only: no logo/image watermark support in this tool.
- Like any visible watermark, a determined user can still edit it out; this is a deterrent, not a security measure.
Examples
Best Practices & Notes
Best Practices
- Use tiled layout if the image might be cropped before reuse, so the watermark survives.
- Keep opacity low enough that the underlying photo is still clearly evaluable; the goal is deterrence, not obscuring the image.
Developer Notes
watermarkJpg reuses the FONT table and glyph-advance math exported from jpg-text-adder.ts, but blends each glyph pixel via a dedicated blendGlyphPixel helper (linear interpolation against the existing pixel) instead of overwriting it outright the way stampBitmapText does, since watermark text needs to stay translucent.
JPG Watermarker Use Cases
- Watermarking proof images before client approval
- Marking portfolio samples shared publicly
- Deterring casual reuse of unlicensed photos
Common Mistakes
- Setting opacity too high, which can make the underlying photo hard to evaluate.
- Using single-centered layout when the image is likely to be cropped, letting the watermark be trivially cropped out.
Tips
- Combine with JPG Quality Changer afterward if you're also downsizing the proof for faster sharing.
- A short watermark text tiles more evenly than a long one; try initials or a short brand name.