Your best bet is to contact the various horse associations to see if they have any royalty-free photos you can use. They may only require that you include the horse's registered name as it also provides some advertising for that breeder.

If you find them online elsewhere, be sure to email the owner of the photo to get specific permission for what you want to use them for, as there have been some items listed as royalty free that actually belonged to somebody else.

Good luck, and let us know how you make out.

__________________
Colleen in Friendly Manitoba...
Proudly selling digital designs at SBB
(Come take a peek at my Gallery or check my BLOG to see what I'm up to)