The footage shows a man in a yellow shirt leaving a backpack in the popular Erawan shrine moments before an explosion went off.
At least 20 people were killed and more than 120 people injured.
In a separate attack hours later, an explosive device was thrown at a pier in Bangkok, but no-one was hurt.
The target of a second bomb attack in Bangkok was a busy pier on the city’s Chao Phraya river – another popular tourist spot.
Witnesses say they saw a man throw a small object at the Sathorn pier in Bangkok.
It landed harmlessly in a canal.
This man was nearby and says if the explosive device had not fallen into the water, it would have caused much more damage and, possibly, deaths.
“I heard the sound of something like an ignition, then I saw smoke first, followed by the sound of an explosion.”
At least 20 people were killed in the earlier bomb blast at the popular Erawan Hindu shrine during the evening rush hour.
Among the locals killed in the attack were nationals from China, Britain, Indonesia, Malaysia, the Philippines and Singapore.
Local residents and tourists have been bringing candles and flowers to the site.
24 year old Tanakit Sinsuwong lost his grandmother in the blast.
He says he’s angry and upset that someone would attack innocent people in Thailand.
“They should not do this to our country. People who are innocent should not be victims. Nobody would want to come to Thailand.”
Security footage shows a man carefully and deliberately removing his backpack inside the shrine, getting up without it and immediately leaving the scene.
The place where he was sitting is where the bomb went off a few minutes later
No group has yet claimed responsibilty for the attack.
Thai Police Chief Somyot Poompanmuang says police are working to identify the man in the video.
“From the closed circuit TV footage, we cannot confirm who that is because in the video the suspect might have disguised himself to mislead the officials. We cannot confirm the identity of the man in the video.”
The attack has rocked tourism and the Thai currency.
Since the attack, the baht fell to its weakest level in more than six years
Tourism accounts for about 10 per cent of the country’s economy.
It’s one of the few industries propping up local business in an economy still struggling more than a year after the military seized power in May 2014, sparking months of street protests.
In an effort to restore calm, security has been increased at transport hubs and tourist sites in the capital.
A spokesman for the Thai Ministry of Foreign Affairs says the government would consider putting soldiers on the streets, if necessary.
“If such incidents occur and the presence of police or military personal could make the people feel safer, then it’s one measure that would be considered. But if the situation is, that the authorities feel is under control, then the police will continue to do their job.”
Thai Prime Minister Prayuth Chan-ocha has been under pressure to improve the country’s economy.
He’s vowed to bring those behind the bomb attack to justice and tried to reassure the safety of foreigners in Thailand.
“In our country there are individuals or groups of individuals who are seeking to destroy the country. The ongoing attempts at destruction might be politically motivated, targeting the economy, tourism for whatever reason. The government will work to find those perpetrators and bring justice upon any networks involved as soon as possible.”
Prime Minister Tony Abbott has urged Australians to continue travelling to Thailand despite the bombing and has offered Thailand assistance.
“Australians should continue to go to Thailand because the object of the sorts of people who let off bombs in crowded cities is to scare us from being ourselves.”
But Hong Kong’s Tourism Council has cancelled all tours to Bangkok.
The Council’s Chief Executive, Joseph Tung, says the Hong Kong government has raised the travel warning to red, which advises against non-essential travel.
“We have basically reached an agreement that tours will be cancelled to Bangkok from this afternoon, 18th of August, until the end of August. All the tours to Bangkok will be cancelled. And I think the main thing is that the Security Bureau show a red travel alert and we also look after the safety of the passengers. So the agents have made such a decision.”