Add watermark and disable right-click

Hi,

I’m trying to add a watermark and disable right-click on the website I’m working on, I found this : https://jsfiddle.net/w5gQS/ but I don’t know where to add the JavaScript code :s

I tried adding it in the header.php file of my theme but nothing happened, if anyone knows how would I manage to make it work that would be great !

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