Those ISIL fighters prominently flying the black flag beloved of the Salafi.
Muslims emulating to the greatest degree possible Mohammad.
It is reputed that Mohammad flew a black flag into battle, inscribed with the Islamic testament of faith: "There is no God but Allah and Mohammad is his Prophet".
"The Black Banner or Black Standard also known as rayat al-`uqab "banner of the eagle" or simply as al-raya "the banner") is one of the flags flown by the prophet Muhammad in Islamic religion, an eschatological symbol in Shi'a Islam (heralding the advent of the Mahdi), and a symbol used in Islamism and Jihadism"
ISIL fighter waving the black flag.
Banner of the Somali Al Shaabab! Seems to be the same as that flag borne high by the ISIL fighter!