Answer:
Yes, copyright should be essential for artwork if you'd like to claim ownership. Although it's not necessary, it is worth the process to go through with. If you're creating simple images for fun I'd personally say it's not worth going through with watermarking, however if you're creating images for professional use, I would 100% recommend copywriting. Secondly yes, copyrighting prevents the duplication of artwork, if anyone tries using your image without your consent you can go through legal action to claim your work.