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