There are numerous ways to copy an image off of the web, so if a person wants your image, they will find a way to copy it. If they really want to claim your image as their own, there are ways to remove watermarks. Depending on where the watermark is placed, one could simply crop it out of the picture. Ultimately, the watermark offers limited protection against theft unless you do a full-page watermark, which almost defeats the purpose of posting it. With that being said, a lot of graphics companies like Adobe Stock and Shutterfly have mastered the art of all-over watermarking without taking away the ability to view the graphic.
I am still of the belief that is it better to use a watermark as opposed to not using one. Unfortunately, the only real way to protect your image from someone stealing it is to not place it on a website or places like social media.
Read more about building a creative reputation with watermarks.
—Just My Imagination DeZigns