A so-called pandering provision makes it a crime to promote, distribute or solicit material in a way intended to cause others to believe it contains child pornography. It carries a sentence of at least five years in prison.
The Supreme Court in 2002 struck down an earlier version of the law that included computer generated images that appeared to depict minors engaged in sexually explicit conduct.
Congress then adopted new legislation in 2003, which President George W. Bush signed into law, in an effort to comply with the Supreme Court's ruling.
But a U.S. appeals court in Atlanta ruled the law still did not pass constitutional muster and violated guarantees that the government cannot suppress lawful free speech.
The Bush administration told the Supreme Court the ruling interfered with the effort by Congress to suppress the market for child pornography.