Unfortunately, no site can protect work from copyright infringers who are adamant on having an image that is on their page.
As soon as you go to a site, the image is on your computer. No right-click or watermark stops that. All images go straight into a temp folder and can be grabbed from there by people who want it. That is how browsers are designed to make browsing and speed more efficient.
I only have to take a screenshot and I have any image I want, from any site.
We do, however, counter this with these options
1. We have no right-click on some pages but all mobiles and some browsers ignore that order. Nothing we can do about that.
2. We offer a watermark, although this does deter buyers.
3. Enlarging any thumbnails degrades the quality of the image terribly so it is useless for a print. Remember if they want the image for a phone wallpaper etc there is NOTHING we can do to stop that, even phones have screenshot takers
4. Your full resolution image is hidden away so people only see the low-resolution copy
5. On the full resolution preview on the main image pages, it only shows a small section and a border is actually removed. That way, even if people took the time to open all the full resolution image and copied each segment to stitch together, they would not get the complete image.
The low-resolution thumbnails and preview images are as safe as we can make them, your full images are not on the site
You need to look on the site which is infringing on the work and find a contact link. Then you need to file a DMCA notice (Digital Millennium Copyright Act)
Unfortunately, these need to be sent in by the artist themselves to the site infringing on them or to the server host of that site.
You can also find that here http://www.whois.com/
Do check it is not on our retailers list first if you are signed up to that https://fineartamerica.com/controlpanel/retailwebsiteprogram.html