Anyone who makes a painting and hangs it in a public space doesn’t have to worry too much about it being stolen (unless you’re a famous artist, of course). The situation is different with work that you post online or on social media. It is not uncommon for people there to make a good impression with work that they have ‘borrowed’ elsewhere. A watermark in your images prevents such abuse. You can do that with TSR Watermark, for example. Unfortunately, the free version also puts its own watermark, but on the other hand, this is one of the most extensively configurable programs of its kind.
TSR Watermark you find here†
Click the link above to download for free TSR Watermark – Adjustable watermark for photos