National Police Office deputy commissioner Pol Gen Ake Angsananond said the photos were from CCTV footage at a Victory Monument coffee shop near the rally site of the the People's Democratic Reform Committee (PDRC).
The suspect in the footage was about 30 years old, wearing a black baseball cap, jacket, white trousers and was carrying a black bag.
In one photo, he was drawing his right arm back, preparing to throw a grenade.
The grenade he threw hit a coffee shop roof and fell two metres from him, near the reporters' tent. The explosion injured 28 persons including one journalist from Post Today newspaper.
Another photo showed the suspect walking away from the scene before throwing another bomb near Rajavithi Hospital to open way to escape.
There were scores of people were wounded at the second blast.
Gen Ake said that the investigators publicise the photos to let the public help give information to police.
He added that the explosive device the bomber used was a GRD 5, the same type used at Banthat Thong on Friday that killed one protester and wounded 38 people.
In related incidents, at around 10.40, a volunteer guard of the Network of Students and People for Reform of Thailand (NSPRT), an ally protest group of PDRC, was wounded in the chest by a gun shot at Makkhawan Rangsan Bridge on Ratchadamnoen Avenue.
Identified as Sitthichai Maliwan, 27, the guard was taken to Vajira Hospital, he returned home after treatment.
Meanwhile, an assailant on a motorbike shot at PRDC guards at the Government Complex at Chaeng Wattana Road but missed the target but hit an electrical post near the barrier. There was no report of injuries.