The man, identified as Antonio R., was in charge of the supply room, ThinkSPAIN reported.
He took photos of basic equipment and combat gear on his phone, and uploaded them onto the site.
In December, the military tribunal sentenced him to three months and one day in prison.
But the Supreme Court judge ruled because Antonio R. had not stolen any items for delivery and a sale and not been made, he was not guilty of any crime.
Although he did take combat gear from the room, the incident was not ruled a crime because he later returned it, ThinkSPAIN said.