How can i add a watermark to an image like 9gag does it

[wademoose]

I need to start watermarking my images as I'm starting to notice people are using them. I really don't like to have watermarks all over an image and took notice at the way 9gag does this which i like. Example: https://9gag.com/gag/352822There isn't any visible watermark, however when you right click and save the image u can see the watermark. How is this done?Thanks guys