Add a watermark to photos: your own logo, many photos at once

The size you choose is a percentage of each photo's width, not a fixed number of pixels. A mark set to 20% covers a fifth of the width on a 4000-pixel camera photo and on a 1080-pixel phone screenshot alike, so a batch of mixed photos comes out looking consistent. The gap from the edge works the same way: it is a percentage of the photo's shorter side.

Your watermark always keeps its own proportions. If the requested width would push it past the margins, as with a wide logo on a tall portrait photo, it is shrunk until it fits instead of being stretched or cut off. Nine positions are available: the four corners, the middle of each edge, and the centre.

Opacity runs from 10% (barely there) to 100% (fully solid). The default is 50%, the half-transparent look most people expect from a watermark: the photo underneath stays visible, but the mark cannot be missed. Lower it for portfolios where the picture should speak first; raise it when you are sending proofs to a client and want the mark to be obvious.

Use a PNG with a transparent background. Transparent areas stay transparent, so only the logo itself appears on the photo. A JPG logo has no transparency: its white or coloured background box is stamped too, at the same opacity as the logo.

Give the logo enough pixels. A mark at 20% of a 4000-pixel-wide photo is 800 pixels wide, so a 200-pixel logo would be enlarged four times and look soft. As a rule of thumb, the logo file should be at least as wide as the mark will appear on your largest photo.

Each photo keeps its format where the browser can write it: a JPG comes back as a JPG, a PNG as a PNG and a WebP as a WebP. HEIC photos from an iPhone are saved as JPG. JPG and WebP are re-encoded once at quality 92 so the photo itself does not visibly change; PNG is lossless. Pixel dimensions stay exactly the same.

Downloaded files get “-watermark” added to the name, so trip.jpg becomes trip-watermark.jpg and your originals are never overwritten. Keep the originals anyway: a watermark cannot be taken back out of a saved photo.

We stamped a 512×512 PNG logo onto two test files at the default settings: bottom right, 20% of the width, 50% opacity, 3% margin. A 1600×1000 JPG of 120,706 bytes came back as a 1600×1000 JPG of 129,816 bytes, about 7.5% larger, because the whole photo is saved again at quality 92. A 1254×1254 PNG grew from 436,475 to 645,259 bytes, about 48% larger, with no loss in quality: the browser writes PNG files with lighter compression than the program that made the original.

Moving the mark to the top left at 30% opacity changed the sizes by about 1% (128,438 and 644,232 bytes). The pixel dimensions stayed the same in every run. If a watermarked PNG is too large for where you are sending it, run it through the converter afterwards and save it as JPG or WebP.

A visible watermark tells people where a photo came from and discourages casual reuse. It does not make copying impossible: a mark in a corner can be cropped away in seconds, and editing tools can paint over it. A larger mark closer to the centre is harder to remove but covers more of the picture. This tool adds only the visible mark; it does not embed hidden watermarks or copyright metadata.