Adding a copyright watermark to photos before uploading them to the internet seems like a sensible thing to do.
It may deter someone from reusing/stealing your valuable artwork.
Here is my suggested method when running The Gimp on Linux.
The idea is to add text that doesn't detract too much from the picture, while also being difficult to edit out of the photo.
I also wanted to avoid doing the whole thing from scratch every time, so storing the text as a brush seemed to be a reasonable approach.
creating the 'brush'
In order to include the copyright symbol, open your word processor (e.g. LibreOffice Writer) and create suitable text, for example:-
© Captain Bodgit
Open The Gimp and use File > New... menu to create a new transparent image (say) 1000px by 200px.
Select the text tool and draw a rectangular text box on the transparent image, then copy & paste your copyright text.
I suggest you select a suitable font, set the text size to (say) 100px and make the text a light grey colour. (Note that you have to block-highlight the text in the text window for any changes to apply to the displayed text)
Save this image as a brush via the File > Export As... menu by selecting File Type (by extension) as GIMP brush and give it a suitable name (e.g. myCopyright.gbr).
Also give this new brush a suitable (and short) Description (e.g. myCopyright).
For Gimp 2.10 this brush should be saved in ~/.config/GIMP/2.10/brushes
...or for Gimp 2.8 this might be:-
Also save the Gimp project (e.g. myCopyright.xcf) in case you want to make some changes or create a second brush using a different colour.
give it a try...
Close Gimp, then re-open and load a suitable photo.
Click on the paint brush tool to select, then click on each of the brushes until 'myCopyright' is displayed as the brush description.
Move the mouse over the photo to check the size of the copyright text. If it is too large, double-click on the brush tool icon to bring up the Paintbrush properties. Change the brush size to suit.
|The copyright text appears as a ghost image until you left-click|
If necessary, play around with the transparency setting to get the desired result. Generally use a transparency below 50% for best results.
If you are not happy with the text size, transparency or position, just hit control-z to delete it and try again.