X-Rays are a valuable tool for helping farrier's trim severely distorted feet, such as the feet of foundered or "navicular" horses. These suggestions help produce films that are optimally usable:

Embed a wire in the "dirt line" around the frog - the deepest point of the collateral grooves. Make sure the wire is all the way into the groove and goes around the tip of the frog at the corium. Use a hoof knife to trim the tip of the frog back to the live sole and remove enough sole to expose the base of the collateral grooves.

Use another metal wire marker to delineate the coronet band and centerline of the hoof at the toe - along the centermost tubules.

Pack the underside of the hoofs with play-dough to help with definition and give the horse something soft to stand on to encourage realistic alignment. Standing on concrete / hard blocks can alter loading and change the pastern axis.

See http://www.hopeforsoundness.com/natbalance/workup/radiographs.html