An image of a Syrian baby's striking scar trailing down what used to be his left eye has sparked a global campaign of solidarity, with people around world posting photos on Twitter of themselves covering one eye.

Amer Almohibany, a Syrian freelance photojournalist documenting Syria's six-year war, said he was haunted by a baby named Karim, who lost his eye and mother in the bombing of eastern Ghouta, a besieged rebel enclave near Damascus.

"His image was permanently etched in my mind," Almohibany told the Thomson Reuters Foundation by phone.