True story from out East: Poet's chapbook is published by a good chapbook press. Has a terrific poem in it that a high-school girl types up as her own and submits to young-people's poetry contests, such as Scholastic's. She wins top prize in THREE contests and $5000. Prizes help her get into a high-prestige school and rev up to become a writer.
Then the little scamp is found out. Publisher can't sue because after publication the rights to the poems reverted to the author. Poet hasn't got a legal leg to stand on: poet did not register a Library of Congress copyright for the individual poem, and probably couldn't have afforded to, at $35 (electronic) or $45 (on paper) fee per poem, a serious artificial difficulty. From the thief they got a written confession (to show her college dean!) and a promise to pay the prize money back to the prize-givers, and that is all.
This is not even an Internet-theft story! It would have been easy and quick to catch such a thief on the Internet; just Google! Want to protect what you have on the Net? Stamp it with your choice of one of the licenses available free from Creativecommons.org.
Stuff you printed, that isn't online -- what this story shows is THAT is now the thing to sweat about!
Granted that this story is a very unusual one, because the poem made money. And it is one of only three poetry-theft stories that I have personally heard about in the past 30 years.