As far as I know, Lenovo Photo Master doesn't have a function to add watermarks to the loaded images. You will need another solution that was developed especially for this procedure, and luckily there are plenty already available for this procedure.
If you follow the next link, you'll see a list with all the applications available to add watermark to.
I've personally used Watermark Software to add some watermarks to my images. You can find it on that list.
