I am not a lawyer, but here is the legal definition of libel.
"to publish in print (including pictures), writing or broadcast through radio, television or film, an untruth about another which will do harm to that person or his/her reputation, by tending to bring the target into ridicule, hatred, scorn or contempt of others. Libel is the written or broadcast form of defamation, distinguished from slander, which is oral defamation. It is a tort (civil wrong) making the person or entity (like a newspaper, magazine or political organization) open to a lawsuit for damages by the person who can prove the statement about him/her was a lie. Publication need only be to one person, but it must be a statement which claims to be fact and is not clearly identified as an opinion. While it is sometimes said that the person making the libelous statement must have been intentional and malicious, actually it need only be obvious that the statement would do harm and is untrue"