It had been nearly a decade since Mahmoud al-Khalaf laid eyes on his father, but he immediately recognised the bruised and battered face in the graphic photograph circulating online. It was one of four published samples from a cache of 800 images allegedly showing Syrians who died in the summer of 2013 in regime detention in the northern Aleppo Central Prison. The Syrian news website Zaman al-Wasl said it had received the full portfolio from a Syrian military photographer who took the images in 2014 and later defected, without disclosing the soldier’s name. A previous batch of photos taken bya…