Here is the full list of all 16 I commissioned some letters achievements.
Complete the game in its entirety.
Find everything hidden in the Post Room artwork.
Find everything hidden in the School Library artwork.
Find everything hidden in the Space Train artwork.
Find everything hidden in the Books And Statues artwork.
Find everything hidden in the Information Liberation artwork.
Find everything hidden in the Floral Front Door artwork.
Find everything hidden in the Sunset At The Park artwork.
Find everything hidden in the The Computer Room artwork.
Find everything hidden in the National Bird Day artwork.
Find everything hidden in the Town Of Owl artwork.
Find everything hidden in the Oversized Library artwork.
Find everything hidden in the Clocks In The Clouds artwork.
Find everything hidden in the Courtyard Play artwork.
Find everything hidden in the Post Lunch Kitchen artwork.
Find everything hidden in the Dressing Up artwork.