If you type in the name of the racehorse into google it might come up with something if not id type in the name of the racecourse then photographer in might bring up something. Generally if the horse never won there prob wont be any photos. Sorry hope that helps
I wish I could remember the name of the chap I contacted about my old horse - I googled his racing name to no avail, then went on the racing post website and found the name of a photographer and emailed him with the horses name and he had loads of amazing photos (not all winning ones either). I could have a look for you - there's a chance I may recognise the photographers name. Will report back in a while!
If you contact the racecourse they can tell you which photographers work there, then you can contact them, I have done this and managed to get photos it does help if you you knew when they ran (you can look it up on the racing post website) as they tend to have hundreds of pictures. hope this helps.