What the watermark tool renders
This page stamps a line of text onto one photo or a whole batch. It is a text watermark only; there is no option to overlay a logo file. The text is drawn with the browser's canvas in a bold system sans-serif font at full image resolution, so the result is sharp on the exported file and not a low-resolution overlay stretched to fit. Drop your files, adjust the settings, press Preview to see the stamp on the first image, and then Apply and download all to process every file and receive them in a single zip named watermarked.zip. Each card in the list also gets its own Download button once it is stamped.
The settings and how they scale
Text is free-form and defaults to a copyright symbol followed by Your Name; replace it with your name, studio, handle or website. Position offers five anchors, bottom-right, bottom-left, top-right, top-left and center, plus tiled, which repeats the text across the whole image at a 30 degree tilt. Size is given as a percentage of the image width, from 2 to 20 percent with 6 as the default, so the watermark stays proportional whether the photo is 800 or 6000 pixels wide; on a 4000 pixel wide picture the default gives 240 pixel tall letters. Opacity runs from 5 to 100 percent with 45 as a sensible middle that reads clearly without hiding the picture. Colour takes any CSS colour, hex codes included; white suits most photos, and a dark grey is better for bright, high-key images.
Because the size is tied to width, a batch mixing landscape and portrait shots will show slightly larger text on the portraits relative to their height. Preview the first file, and if the batch is mixed consider running portraits separately with a smaller size. The font is whatever bold sans-serif your operating system provides, so the same settings look marginally different on a Mac and on Windows.
What comes out and what it costs in size
Every stamped image is saved as JPEG at quality 92, with -wm appended to the name. A typical 4032x3024 phone photo of 2.8 MB comes out around 2 to 3 MB; the watermark itself adds almost nothing, and the size is driven by the re-encode. A batch of 30 such photos gives a zip of roughly 60 to 90 MB, built in memory in the browser, so a very large batch on a phone can run out of memory; on a laptop a few hundred photos is fine. If you need smaller files, send the zip contents through the compressor afterwards, where you can also switch to WebP.
The JPEG-only output has two consequences. Transparent PNG sources lose their alpha channel, and the transparent area is filled black by the browser encoder, so watermark PNG graphics elsewhere and use this page for photographs. And metadata is dropped: the exported files carry no EXIF, no GPS and no colour profile, which is usually welcome for images headed to a public gallery.
Corner stamp or tiled pattern
A single corner stamp at 40 to 50 percent opacity is what most photographers use; it credits the work without spoiling it, and it can be cropped off, which is the accepted trade-off. The tiled mode is the deterrent option for proofs and previews sent to clients: repeated diagonal text covering the frame cannot be cropped away and is tedious to clone out. Set it to 15 to 25 percent opacity so the client can still judge the photo. Neither approach is a technical protection; a watermark is a signal of ownership, not a lock.
All rendering, zipping and downloading is done locally. The photos never leave the browser, which matters when the batch is client work you are not allowed to hand to a third-party service. For sizing images before stamping, the resize tool has the common social presets, and the social media image sizes guide explains which size each platform expects.