The photo shows Mussolini and his supporters in Italy. A photo of Benito Mussolini and other men marching. All of them are wearing black shirts. Many of the men are holding banners. Supporters who used violence and intimidation to help Mussolini seize power were called

They are called Black shirts

Explanation:

Mussolini, who was the Fasist leader during his reign in Itlay was a tyrant who seized power from Rome. He adopted violewnce and intimidation before his successful power grab.

To be successful, he had to encourage people who shares similar fascisim views with him to participate leading to creation of supporters. These supporters are commonly called Black shirts due to the mode of their dressing style.