How can i protect original product images?

I enabled watermark funtion of Magento, but original files still accessable from url without watermark.

Example:

Cached image url with watermark

/pub/media/catalog/product/cache/df484df48ez74849c15sd4f7780/f/f/dsf-8f48d4f.jpg

Original image url without watermark:

/pub/media/catalog/product/f/f/dsf-8f48d4f.jpg

So, if someone remove /cache/df484df48ez74849c15sd4f7780/ from url can access to original photo without watermark to steal images.

How can i protect my original images?