The Kommersant newspaper published a photograph of Dzhennet Abdurakhmanova posing with a handgun. A man with his arm around her, also holding a gun, is identified as Umalat Magomedov, whom the paper describes as a militant leader killed by government forces in December.
The picture was sent to Moscow police, together with biographical details about Abdurakhmanova, by Dagestan's ministry of internal affairs, Kommersant said.
Police investigating the blasts, which killed 39 people and injured 70, believe Abdurakhmanova was one of the two female bombers, according to the Russian newspaper Kommersant.
Abdurakhmanova is thought to have carried out the first suicide attack, which killed more than 20 people at Lubyanka subway station, Kommersant said. The identity of the second attacker at Park Kultury station is not yet known.