Long story short – if you photo is out there people can and will steal it! You can do nothing about it!
The extreme limits someone can go to copy your photo!
What you can - and must - do is to make it harder for the thieves to use your photo. And you do that by adding a watermark. A visible watermark that is so hard to remove, it’s not worth the time!
Have a look at these photos with watermarks, even if you download them you can use them without telling the world who they originally belong to. Not good if you are going to use for business purpose isn’t it? If you try to remove the watermark you end up damaging the aesthetics of the image cropping out most of it rendering the image useless.
So a watermark discourages unauthorized use of the photos by making the watermarked image useless for the person downloading them. People would rather find an image they can use straight away than spending hours to remove a watermark from an image in Photoshop.
If your business depends on photos, you better add watermarks.