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I looked into it a bit earlier, it is possible but not straight-forward. When you right-click an image on the website, it's often not actually an image in the way browsers understand it, or it's low quality and the 'Best Image Quality' option overwrites the link with a higher quality version.
Adding a 'Copy Image' option would need to trigger a download, so it wouldn't appear in your clipboard immediately; that would be especially noticeable with slow internet speeds and large images, so I need to figure out some UI to notify people whenever something starts and finishes downloading.