Ministry spokeswoman Karolina Gałecka said on X on Monday that the picture was manipulated image and that officials were securing evidence.
She added that there would be "zero tolerance for this kind of primitive behaviour."
She said the image had been shared by, among others, accounts linked to the right-wing TV channel Telewizja Republika, including one belonging to its journalist Sławomir Jastrzębski.
Six people were killed and 16 injured on Saturday when a 24-year-old man drove a car into Kraków’s Main Square and opened fire at random with an automatic weapon.
The injured included two police officers and the attacker, who died in hospital early on Monday.
Police also found the bodies of three of his close family members at their home in Ostrowiec Świętokrzyski.
The Polish Press Agency (PAP) said an analysis using SynthID had detected the use of OpenAI tools to create the fake image of Interior Minister Marcin Kierwiński.
It was based on a genuine photograph published on Facebook in April 2024, which showed Krzysztof Kucicki, a candidate in that year’s Warsaw local elections.
Justice Minister Waldemar Żurek said prosecutors would examine cases of disinformation surrounding the attack to determine whether any amounted to a criminal offence.
A second AI-generated image, shared on Telegram, showed a masked man in uniform wearing a Ukrainian flag patch, with Poland’s coat of arms in the background.
It carried the caption "Thanks, dad, for the gun" and was falsely presented as a photo of the attacker.
The same SynthID analysis found it had also been created with OpenAI tools.
Ukraine’s Centre for Strategic Communications and Information Security said the image had been viewed at least 10 million times on social media within 48 hours.
Poland's research institute NASK identified about 2,000 accounts spreading disinformation about the attack.
They included automated bots posting mainly in Polish, English, French and Dutch.
Deputy Prime Minister and Digital Affairs Minister Krzysztof Gawkowski said on Sunday that dozens of the accounts used Russian-language content or made references to Russia.
He said this warranted particular attention, but did not in itself establish who was behind the campaign or whether it was coordinated.
(ał)
Source: PAP