SITE, which studies terrorist activities, released the photos on its Twitter account around 10pm on Saturday.
Its co-founder Rita Katz, whose activities have aroused suspicion among Bangladesh officials, said in a tweet that Middle East-based radical group Islamic State, which has claimed credit for the massacre, released the photos.
The identities of the persons in the undated photos were not provided.
Another group of terrorism observers, Terrorism Monitor, identified the same persons as Abu Omar, Abu Salam, Abu Rahim, Abu Muslim, and Abu Muharib al-Bengali.
Later on Saturday night, Bangladesh Police published photos of five suspected attackers killed in the military operation to rescue the hostages.
It is not clear whether the other photo published by police is of the same person whose photo IS released.
Army commandos raided the cafe in Dhaka’s diplomatic heart of Gulshan on Saturday morning, ending a 12-hour bloody hostage crisis.
They found 20 bodies and initially said all of them were foreigners. A later statement, however, indicated Bangladeshi deaths as well.
The authorities said six attackers had been killed during the assault and another captured alive.
Later, police chief AKM Shahidul Hoque said five of the dead gunmen were listed as militants and police had been looking for them.
IGP Hoque spoke to journalists after the funeral prayers of two policemen, who were killed when the attackers threw grenades at them in an early skirmish when the terrorists had stormed the cafe.