Yes, conformation is all based on the difference in size between different parts and the angles of things...this is almost impossible to judge in a picture unless the horse is set up balanced and square on a flat surface...in person, you see the horse at many different angles, so you can compensate. In a picture, we only get one angle...so its got to be the best one possible.
• You need help with this. Either get someone to man the camera or hold the horse. If they are holding the horse, it needs to be someone with knowledge of horses and what you are trying to accomplish.
• Shoot in the morning or late afternoon when the sun is at an angle (especially if your horse is dark bay or black). If you are more camera savy, you can also use a flash to fill in dark shadows. Oh, and don't shoot into the sun.
• Sit in a chair or kneel to take the photograph: get on the same level with your horse's body.
Side View: Notice the hooves are completely even in both photos. Also, you want the horse looking ahead, not pointing his nose at the camera. The horse below is not really standing square, but its still a fine stance for judging conformation. More important that they are not leaning backwards or forwards.
The horse below is standing a little under herself in front, but still acceptable.
Front View: Chest, front legs, hooves. The horse is square.
Photo below is barely acceptable: very dark and hard to pick out details.
Rear View: Hindquarters, back legs, hooves. You may have to pull the tail out to the side for a clear shot. Again, horse stands square.