Christ.... people can't READ huh? So here's how to unlock the CG. And if you're wondering why it's in english, that's cause I'm using MTOOL to play this. "Pappy" should be called "Puppy" but MTOOL's free translation is on par with MTL
Also, spoiler tagged to condense the post space.
Step 1: BEAT THE INTRO CHAPTER. You need access to the city.
Step 2: GO HERE
Step 3: GO HERE (might need to beat up the guys attacking the homeless people first)
Step 4:
GO BEHIND THIS TREE. THE ENTRY INTO THE GALLERY ROOM IS HERE!
Step 5: Follow the path til you go down these stairs
Step 6: Enter this door
Step 7: ACTIVATE THIS SWITCH HERE!!!
FINAL STEP: You view the gallery here on the menu (default PC controls is the X key) if you've done everything right. Feel free to save the game when it's all opened up too.
YOU DO NOT NEED A FULL SAVE TO DO THIS!!!
Hope this finally helps. too many were asking how to do this and simply not following what was said. you have images now so that's on you if you still can't unlock the gallery w/o playing the game.