From the BBC:

Andrzej Marek again proclaimed his innocence as his three-month prison term began in Szczecin on Monday.

He was convicted in 2002 of libelling an official in the town of Police by saying the man used his position to promote his advertising business.

Rights groups have protested against the sentence, noting he is the only person in the EU imprisoned for libel.

Ann Cooper, the executive director of the Committee to Protect Journalists (CPJ), said she was "deeply troubled" by the court ruling.

"This case demonstrates the urgent need for Polish authorities to eliminate laws that criminalise libel," she said in a statement before Marek was jailed.

Poland is not a hotbed of free expression. Check out this earlier posting.