In Batman Arkham Origins Blackgate, Hidden pieces of evidence are scattered throughout Blackgate, also known as Detective Cases. When you find all the pieces of evidence for a single detective case, Concept Art is unlocked. There is a total of fourteen Detective Cases:

Ground Zero
The Joker is Wild
Kidnapped
Sixty Feet Under
Bird of Prey
Breakout Break-In
No Laughing Matter
Cell Block Bird Cage
Final Stand
The Bidding War
Doctor's Orders
A Life on the Line
Power Play
Information Gathering