You only want to give '/images/prova.jpg' to the <img> or image_tag. The value is going to be interpretted by the browser so that PATH is not a URL. Unless your routes are also set up to catch this and you're finding the file and using send_file() to get it back. (NOTE: I'm *not* recommending this!)
It looks like you should remove RAILS_ROOT+'/public' from all of your "url"s
-Rob
Rob Biedenharn http://agileconsultingllc.com Rob@AgileConsultingLLC.com