How do watermarks work?

Question

Photo

I often heard about watermarks and they are also added to the video, but how can they protect if they are easy to remove or replace with your own mark?

Answer 1

There are different types of image marking, which are called the term watermark, but which have nothing in common with each other.
It is impossible to simply take and remove, say, even a translucent inscription on an image, because when it is superimposed, information is lost, which can be restored, but only by thinking out the missing details.
But there are also other ways that are based on various mathematical operations on image data. Such modifications cannot be seen with the eye, but if one knows that they have been made, one can easily detect them. Some of them are detected even if only a fragment of the image is analyzed or if the image has been reduced/enlarged or recolored. Since these algorithms are most often associated with the frequency decomposition of the image, to understand their principles, you need to understand a little in this area of ​​\u200b\u200bmathematics.