An image crystal was a still holographic image. In the aftermath of the battle of Endor, Grand Admiral Rae Sloane searched the Hall of Imperial Register for information on her superior, Admiral Gallius Rax. There, she encountered an image crystal depicting a young Rax alongside ISB Colonel Wullf Yularen, Admiral Dodd Rancit, Vice Admiral Terrinald Screed, Grand Vizier Mas Amedda, and Galactic Emperor Sheev Palpatine.
By the time of the Battle of Endor, image crystals were considered somewhat antiquated, as more efficient means of data storage had become commonplace.