OK, I may be wasting my time as I know if you can see it in a browser you can copy it.
JavaScripting to block a right-click and copy is very easy to overcome and very frustrating for the end-user who may legitimately want to copy some text from the page.

The following page, https://shared.xara.com/chPPf5WSXN, has an image I have worked on.
It has a copyrighting line of text and a sort or watermark pattern.
You can right-click anywhere but never copy the image.

Now anyone can snip this image but if they used it as there own they would have to remove the copyright else someone might tell on them.

What I am after is what efforts you have to go to remove the notice and the watermark pattern so it seems like an original copy.
You could try mangling the HTML code - try and see where you end up.
I am hoping to see that the effort to rip off an image is time-consuming enough to offer a modicum of protection from theft.

Any resultant uploads should be 1200x760px so I can compare to the original.

I will explain how to make a pattern that could match your site's favicon.

I have been developing a drop-in replacement for existing site images that use Xara's Live Copy. Unfortunately, in doing so I have uncovered a small clutch of issues that scupper that approach; one day, they might be overcome...

Acorn