The media did not name the man, and Iran’s judiciary has yet to comment.
“The German national was detained while taking photos of Aghajari oilfield in Khuzestan province,” the report said.
Iran has detained scores of foreign and dual nationals in recent years, in many cases accusing them of espionage — charges condemned as baseless by experts and rights groups outside the country.
Foreign governments have often characterised those detained as hostages, used to secure diplomatic leverage. Iran has detained three German-Iranians in the past year.
Iran also holds three French nationals, with one man, Benjamin Briere, sentenced to eight years in jail on spying charges.
Last week, Iran executed British-Iranian citizen Ali Reza Akbari, having accused him of handing secrets to the British government. Mr Akbari’s execution was widely condemned by the UK, US and EU.