At FCO, do the self serve ticket machines take cash? I saw a youtube video that showed that thy didn't
Check the roninrome.com site for info - the machines did take euro a year ago (and gave change up to €20), but that may have changed. If the machine has pictures of coins and bills and no sign saying otherwise, it should take cash.
In general, there are self-service ticket machines that take cash but I don't know specifically about the FCO ones. If they do accept cash, like Zoe said there will be a symbol of cash in a circle at the top of the machine. (see this picture
to see what I mean)