Copyright infringement is not so easy to prosecute as you might imagine. For a court to proceed there has to be proof that the song was not only used without permission, but that the person committing the infringrmrnt profited by the performance monitarily and that the copyright holder suffered either monitarily or otherwise (i.e. reputation, defamation of character etc.) In many (if not most) situations, the errant performer can make amends with a public apology (whether or not it is accepted). Protecting yourself from prosecution can be as simple as naming the tunesmith "This next song was written by Bob Dylan ..."

Sing and be damned.