keptlocal
· 3 min read · Image

How to Watermark a Photo for Free

HP
Hitendra Patel
Founder, keptlocal · Senior Technical Lead, Healthcare IT

Sharing a photo publicly — a portfolio preview, a proof for a client, an image meant to be attributed if reposted — often calls for a visible mark showing where it came from. Here's how to add one without an image editor.

Watermark a photo in your browser (no upload, free)

The Image Watermark tool on keptlocal stamps text onto a photo with a live preview, entirely on your device.

  1. Drop your photo onto the tool.
  2. Type the watermark text.
  3. Pick a color and a position — a diagonal center mark, or a corner/edge placement.
  4. Adjust size and opacity while watching the live preview.
  5. Click Download.

Diagonal center vs. corner placement

A diagonal watermark across the center of the frame is the standard choice for stock photo previews and portfolio proofs, for a specific reason: it can't be cropped out without also cutting away the photo's main subject, which sits in the center of most compositions. A corner placement is much easier to crop off entirely, which makes it a weaker deterrent — but it's also far less visually intrusive, which is the right tradeoff when the goal is attribution (a website URL, a handle) rather than actively discouraging reuse.

Getting the opacity right

Too low, and the mark is barely visible — easy to miss, and not much of a deterrent either. Too high, and it competes with the photo itself for attention, defeating the purpose of showing the work in the first place. Somewhere around 20–30% opacity tends to be the sweet spot for a mark that's clearly visible without seriously interfering with viewing the image — adjust from there depending on whether the priority is subtlety or visibility.

Privacy: what happens to your photo

The watermark is drawn directly onto the image using the Canvas API — your photo is never uploaded. Open DevTools → Network while using the tool and you'll see no outbound requests, which matters if the photo itself is something you'd rather not send through a third-party server before it's even published.

Watermark a photo now with keptlocal's free Image Watermark tool — no upload, no signup.

Frequently asked questions

Does a watermark actually stop people from using my photos?
It discourages casual reuse and makes unauthorized use easy to spot, but it isn't a technical barrier — someone determined can crop it out or edit around it, especially a corner-placed mark. A diagonal center watermark spanning the frame is much harder to remove without visibly damaging the image.
What size and opacity should I start with?
Around 6% of the image's shorter dimension for size, and 25-30% opacity, is a reasonable starting point for a visible-but-not-overwhelming mark — adjust from there based on the live preview.
Can I watermark multiple photos at once?
This tool processes one image at a time so you can preview and adjust the exact placement for each photo. For batch processing many photos with identical settings, that's a workflow this tool doesn't currently support in one pass.
Will the watermark show up if someone screenshots the image instead of downloading it?
Yes — the watermark is part of the rendered pixel data, not a separate overlay layer, so it appears in screenshots the same as in the original file.
Does adding a watermark change the image's file size significantly?
Only marginally — the watermark text adds a small amount of additional visual detail for the encoder to represent, but the effect on file size is minor compared to the image's overall content.
Free browser tool
Image Watermark

Stamp text across a photo — free, in your browser.

No upload. No signup. Runs in your browser.

Use Image Watermark