The paintings and posters will be awarded as you progress through the game on any difficulty, while the pinups will be awarded for playing the game on hard difficulty. There are a total of 8 paintings, 10 posters, and 14 pin-ups. They can be accessed in the game menu under extras.
Paintings
Painting #1 Unlocked in Chapter 3
Painting #2 Unlocked in Chapter 5
Painting #3 Unlocked in Chapter 7
Painting #4 Unlocked in Chapter 9
Painting #5 Unlocked in Chapter 10
Painting #6 Unlocked in Chapter 13
Painting #7 Unlocked in Chapter 14
Painting #8 Unlocked in Chapter 15
Posters
Poster #1 Unlocked in Chapter 2
Poster #2 Unlocked in Chapter 2
Poster #3 Unlocked in Chapter 4
Poster #4 Unlocked in Chapter 6
Poster #5 Unlocked in Chapter 8
Poster #6 Unlocked in Chapter 11
Poster #7 Unlocked in Chapter 12
Poster #8 Unlocked in Chapter 13
Poster #9 Unlocked in Chapter 14
Poster #10 Unlocked in Chapter 15
Pinups
Pinup 1 Chapter 2: Home Sweet Home
Pinup 2 Chapter 3: Enemy of the State
Pinup 3 Chapter 4: Murphy's Law
Pinup 4 Chapter 5: The Buzzsaw
Pinup 5 Chapter 6: Time Well Spent
Pinup 6 Chapter 7: In Loving Memory of Francesco Potenza