Disable right mouse click
Disabling the right mouse click and with this the appearance of the context menu (which leads to a direct download option for photos) will not prevent anybody from actually doing so.
As soon as the browser is loading the data and displaying photos, they are downloaded to the client and are able to be extracted by anybody, even with built in browser tools.
If you still want to prevent users from right clicking, add following code into the code settings of your project / side wide code.
document.addEventListener("contextmenu", function(e){
e.preventDefault();
}, false);
A stack setting exists therefore already for Gallery Stack.