Cheat codes:

Unlock Cireka's Vow Drizzt's Journal book:
Complete Stand at Mithral Hall level

Unlock Illius' Youth book:
Complete The Jungles of Chult level

Unlock Khelben's Letterbook:
Complete The Wizard's Tower level

Unlock Nesme's Fall book:
Complete The Yuan-Ti Temple level

Unlock Ygorl And The Dragon book:
Complete Into the Underdark level

Unlock Zhai's Past book:
Complete Attack at Cedarleaf level

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