The photograph published and Russian media saying that police are searching for a connection with the attack.
It shows a man with a black hat and beard. The media say the man entered the Petrograd station, 20 minutes before the blast, transferred agencies.
Interfax news agency earlier said the surveillance cameras captured suspect the blast.
Ten people were killed and fifty wounded in the blast in metro St. Petersburg that the Russian authorities are investigating as a terrorist act.
Russia declared three days of mourning.