Successfully complete the following levels to unlock the corresponding picture in the gallery:

War in Damara: Battlefield
Gemspark: Concept Art
Attack at Cedarleaf: Cedarleaf
The Wizard's Tower: Wizards Tower
The Jungles of Chult: Chult Jungle
The Yuan-Ti Temple: Chult Temple
Stand at Mithral Hall: Mithral
Into the Underdark: Githyanki Outpost
The Dragon's Lair: Dragon
The Lord of Chaos: Limbo