These diagrams show the bone structure differences between toed in and toed out.
These three horses are wider at top so they toe out.
This horse also has a deviation in his leg plus a rotated cannon bone. If you trim this horse to stand straight you will make him sore. But if you balance him to his cannon bone he WILL stay sound.
This x-ray shows a medial-laterally balanced foot the lines between the bones are even. On a unbalanced foot they will be compressed on one side and open on the other. This foot was balanced using a T square.
When viewing a horse from front look for deviation rotations and offset knees.This will help you to see why the horse is toeing in or out.
The black horse is a perfect example of diagram on the left.