Free images results:

Mule pictures, stock photos and images


Donkey Royalty Free Stock Photos
Author: Jetr001

Also, here are some commercial RF-licensed images that match your search criteria:  
Mule Deer Stock Photography
Author: Iorboaz
Mule Deer Royalty Free Stock Images
Author: Truan
Mule Stock Images
Author: Mokreations
Mule days Royalty Free Stock Images
Author: Rancho
Mule Stock Photos
Author: Splosh
Mule Deer Stock Photo
Author: Iorboaz
Mule Stock Image
Author: Laozhang