The work was described by art curator Vittorio Sgarbi, who organized the 'Museum of Madness' exhibition, as "crap".
"It's a piece of crap; a painting by a desperate man," said Sgarbi. He was speaking ahead of the exhibition's opening on Saturday at the Museum of Salò, housed in a former church near Brescia.
"You don't see greatness [in the painting], but misery. It's not the work of a dictator but that of a wretch," he added.
The oil painting has never been exhibited to the public before but has been loaned to the museum by a private German art collector, and will form part of an exhibition on 'political madness'.
Altogether, around 200 paintings, photos, sculptures and multimedia installations will explore the theme of madness at the museum until November 16th this year.
The exhibition's organizers noted that Hitler once told British Ambassador Neville Henderson: "I am an artist, not a politician. Once the Polish question is resolved, I want to end my life as an artist."
The northern town of Salò has a close connection with the history of fascism, and was the seat of government in Benito Mussolini's Nazi-backed Italian Social Republic between 1943 and 1945. The state was informally known as the Republic of Salò, a nod to the town where Mussolini and his foreign ministry had their headquarters.
Perhaps for this reason, recent years have seen Hitler supporters in Lombardy gather prominence, with some representatives being elected to local governments including Como and Novara. In 2014, Milan-based supporters emblazoned the town with posters praising Hitler, to celebrate the 125th anniversary of his birth.
And last year, right-wing Milanese newspaper Il Giornale gave out free copies of his autobiography, Mein Kampf, a move which was denounced by then-Prime Minister Matteo Renzi and representatives of Italian Jewish organizations.
"Know it in order to reject it," was the justification given by the newspaper, which said the free gift was an attempt to educate readers on "the toxicity of national-socialism".