Disable "Select Thumbnail" menu option?

Tinkering around with the config.thumbnail options in the config file (config.cfm for me, using CF), I'm not finding a way to disable the "Select Thumbnail" option in the menu that pops when right-clicking a thumbnail of an image in one's library.

It's something that could well cause issues with my system should a client select a thumbnail of their image instead of the image itself.

I'm not finding any helpful info in the docs, nor in the forum.