How can I add a copyright watermark?

Now I know my work isn’t that good that I need to worry about it massively at the moment but I did a quick internet search and about 100 different apps that work with Windows 10 or whatever it is that now tries to make my laptop look like my mobile (see you are up a bit of a techno-phobe here). So what I really want to know is how can I easily add the copyright of my name to an image before uploading it on to social media or my blogs? Is there a preferred or better app?

Is there a functionality in Twinui (I think this is the default on my lap top) that does it?

Any help and advice greatly appreciated!