Image provided by Cubadebate shows Cuba's President Raul Castro (L) shaking hands with US President Barack Obama during their meeting at the Palace of the Revolution, in Havana, capital of Cuba, on March 21, 2016. Barack Obama on Monday paid tribute to Cuban national hero Jose Marti in Havana, starting the official program of his historic visit to Cuba to strengthen the approach between the two countries. [Photo/Xinhua]