This term refers to special signs or symbols placed on images. It is generally used by placing the logo of the site on the image to prevent an image published on the internet from being published on other sites or to show which site was the first to broadcast even if it was published.
The content of the information can be anything, whether it is a secret message, various algorithms are used when embedding your watermark in your document. No algorithm is 100% secure yet.t to broadcast even if it was published.
Applications such as Photoshop or Pixelmator can be used for Watermark. Also the app called Watermarker is just one of the dozens of apps available for this job on the Mac App Store and is the easiest to use. Thanks to Watermarker, we can add the text or image we want as a watermark to the corners or the middle of a picture.