Mary Blair - Ichabod Crane and the Headless Horseman, 1949
"The Adventures of Ichabod Crane" Animation Concept Painting Original Art (Disney, 1949). Ichabod Crane finds himself sitting backwards on his horse with the Headless Horseman close behind. Rendered in tempera on heavy illustration paper, the art has an image area of 8" x 7".
Wikipedia article on the artist here.
See more Blair paintings in this post at Eaten By Ducks.