The picture - of the BJP's Rajnath Singh offering a laddoo to the CPM's Prakash Karat - was removed by Trinamul in the evening, an hour after the BJP tweeted both the fake and the original, which shows that the laddoo was being offered to Prime Minister Narendra Modi, not Karat.
"Two videos and 6 pics were shown at our press conference. We removed one pic immediately when our research team learnt it was photoshopped," Trinamool said in a statement, without explaining where the fake picture had come from.
SPOT THE DIFFERENCE
A copy of the picture which the BJP said the Trinamool Congress had initially publicised. Trinamool later withdrew the picture. The BJP tweeted the picture with Prakash Karat’s face circled and the original photograph placed alongside to show that Rajnath Singh was offering.
The news conference where the photograph was shown was held around 2pm by the Trinamool's leader in the Rajya Sabha and spokesperson, Derek O'Brien, at his office. It was posted on the party's Facebook page around 5pm.
The BJP exposed the altered picture around 5.45pm and tore into Trinamool on social media, with #fakeTMC trending on Twitter.
"A party which claims that the Narada tapes were doctored is using a morphed photograph. They know they are losing ground and have taken to desperate measures," said Sidharth Nath Singh, the Bengal BJP co-minder.
The party said it was consulting legal experts to take the matter forward.
Karat also issued a statement, saying: "I have not got any opportunity of meeting Rajnath Singh ever. It is a patently false picture."
Around 6.50pm, Trinamool took the picture off its Facebook page and issued the clarification.
"As soon as we came to know that the picture is morphed, we removed it. The matter should end there," PTI later quoted O'Brien as saying.
"We got the picture from the Internet. How would we know that the picture is morphed? We did not morph the picture. It was there on the Internet. They are making a mountain out of a molehill."
In her election campaign, Mamata Banerjee has been alleging a BJP-Congress-CPM nexus and contending that the Narada sting operation was a conspiracy of the three Opposition parties.
Some of the other pictures that Trinamool released on Saturday were of CPM general secretary Sitaram Yechury and Congress president Sonia Gandhi greeting L.K. Advani and Modi. The videos it released were of Congress vice-president Rahul Gandhi's speeches in Kerala, where his party is fighting the Left.
"There was no need to do this (use the fake picture). Now we stand accused of doctoring photographs to malign the Opposition," a senior Trinamool leader said, accusing the party's publicity team headed by O'Brien of causing the damage.
In 2012, months after she came to power, Mamata had come to be identified by the phrase "sajano ghatana" (fabricated incident), which she first used to describe the Park Street gang rape.
A section of Trinamool leaders said the campaign of the Congress and the Left on "Mamata-Modi bonhomie" had forced the party to draw up a counter-campaign to embarrass the Opposition.
Congress vice-president Rahul Gandhi, in Bengal for the last day of campaigning before the fourth phase of polling, again bracketed Mamata and Modi together. " Idhar ek vyakti ka raj hai. Aur udhar unke mitra Narendra Modi hain (Here, there is one person's rule. And there is her friend Narendra Modi)," Rahul said at an election rally in Shyampur, Howrah.
The video war spilled to Delhi, where the Congress released a clip from an old Mamata interview on BBC, where the Trinamool chief had described the BJP as her "natural ally". "In politics, options are always open. But we cannot align with the CPM. The BJP is a natural ally," she is heard saying.
Congress spokesperson R.P.N. Singh said: "Mamata's attack on Modi is a sham. They are speaking against each other to polarise Bengal voters. After the polls, they will come together."
He added: "We are telling Bengal voters that voting for Trinamool would strengthen the BJP and vice versa."