The US state of Georgia's supreme court has dismissed an obscenity case against a man who sent a woman an unsolicited photo of his tattooed penis in a text message.

The court ruled unanimously that the 1970 law applied only to "tangible" material sent through the post.

Charles Lee Warren faced up to three years in prison.

Mr Warren was arrested after he texted the photo in October 2012 and the woman went to the police.

The obscenity law under which he was prosecuted makes it a felony to send unsolicited material depicting nudity or sexual conduct unless the "envelope or container" in which it is sent bears a warning in "at least eight-point boldface type".

The arguments in the case were heard in front of the Georgia high court in November.

On Monday, the court said the case was not being dismissed merely because electronic text messaging did not exist in 1970 when the law was passed.

"The specific prohibition is clearly aimed at tangible material that is delivered in a tangible manner... and because appellant did not send anything through the mail, he did not violate this prohibition," reads the opinion, which overturned a lower court's decision.

"This conclusion is reinforced by the fact that the imprinted notice on the envelope or container must be in 'eight-point boldface type' and must say that the 'container' should be 'returned' to the sender if the addressee does not want to 'open' it."

The state has no other law governing these types of cases, a spokeswoman for Georgia attorney general's office told the Reuters news agency.

Legislation has been proposed in Georgia to amend the law to include pictures transmitted electronically, but it has not been passed.

According to prosecutors, Mr Warren's penis was tattooed with the phrase,