Le Pen has argued that she shared the images in response to a French journalist who drew a comparison between IS and her party.
"I thought I had a right to everything: but, no!" Le Pen suggested the case was part of a smear campaign against her to damage her credibility.
"Words fail me! Solidarity with her and with the French who love freedom", Salvini said.
Le Pen, 50, said she will refuse to have the psychiatric testing.
The photos showed a Syrian soldier crushed alive under the tracks of a tank, a Jordanian pilot burnt alive in a cage and US journalist James Foley, decapitated with his head placed on his back.
Just weeks after a series of terror attacks in Paris that year, Ms Le Pen also shared photos of a man in an orange jumpsuit being run over by a tank and a Jordanian pilot being burned alive in a cage.
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The risk of environmental damage mounted, as human and animal waste was washed into the swirling floodwaters. Some areas are still on on high alert due to the ongoing threat of flooding as rivers and lakes crest.
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He has spent hundreds of millions of dollars on art, including a Jean-Michel Basquiat painting the bought for $110.5 million . SpaceX has not announced how much Maezawa is paying for his trip. "I choose to go to the moon with artists".
Among the list of concerns were whether Le Pen is "in a unsafe state from the standpoint of psychiatry or forensic science".
But it doesn't look like Le Pen will be making an appointment with any psychiatrists.
News of the investigation came on Thursday after the nationalist tweeted "the "justice" department is submitting me to a psychiatric evaluation!".
FILE - In this Tuesday, July 31, 2018 file photo, Marine le Pen, French Member of Parliament and president of the far-right "Rassemblement National" party attends a no confidence session at the National Assembly, in Paris.
Le Pen, though, may see an opportunity to score political points with her base.
Le Pen and her populist party have long insisted they are being unfairly persecuted by France's courts and political establishment as a means to marginalize them. She later deleted the tweet showing Foley at the request of his family, and said she had not been aware he was in the photo.
The crime carries a prison term of up to three years in prison and a fine of 75,000 euros ($91,000), according to the report.