Here is how you can find it.

• First, in Steam, go to Settings -> Storage. There you can see the path for your library.
• Click … icon and select Browse Folder
• Open compactdata folder
• Open folder 3119540 (3119540 is Steam ID number for Scriptorium)
• Open folder pfx
• Open folder drive_c - this is emulated C drive of the game
• Most probably pictures are in users/steamuser folder somewhere