A watermark that looks the same on every photo
Size and margin are measured against the shorter side of each image, not in fixed pixels. A small phone picture and a 24 megapixel camera shot therefore get a watermark of the same visual size in the same spot, so a whole product range or photo set looks consistent after one batch.
The preview shows your first image with the current settings and updates while you drag the sliders. When you let go, every file in the list is processed again with the new settings.
Text or logo
A text watermark is drawn with the fonts of your device, so any language works: accented letters, Cyrillic, Greek, Arabic, Chinese or Japanese. Choose sans, serif or monospace, bold or regular, any color, and an optional soft shadow that keeps the text readable on light and dark parts of a photo.
For a logo, use a PNG with a transparent background. A JPG logo brings its white box along, which shows as a pale rectangle on the photo. SVG and WebP logos work as well.
Corner mark or repeated pattern
A small mark in a corner signs the picture without getting in the way, which suits portfolios and social media. Turn on Repeat across the image to fill the whole picture with a tilted pattern. That is much harder to crop or retouch away and is the usual choice for proofs, previews and photos of documents you send to someone.
JPG, PNG and WebP keep their format. HEIC and AVIF photos are saved as JPG and GIF or BMP files as PNG, because browsers cannot write those formats.