Keep computer locked in a view-only state
Take a look at the xtrlock package, available in the Ubuntu repositories. I think it will accomplish what you're looking for.
You can view its manual page online here: http://manpages.ubuntu.com/manpages/trusty/en/man1/xtrlock.1x.html
While xtrlock is running, the mouse and keyboard are grabbed and the mouse cursor becomes a padlock. Output displayed by X programs, and windows put up by new X clients, continue to be visible, and any new output is displayed normally. The mouse and keyboard are returned when the user types their password, followed by Enter.