Wow, that's a pretty big project to take on. Good luck with it.
I know you said just one picture, but I couldn't decided which one to use. So just pic the one you like best out of these two.
This is the horse I am working with right now (not mine but I've put a lot of work into him and I've posted about him quite a bit on here). His name is Pride, he's a Percheron/Arabian cross. That's his mother, Rose, in the background. You can edit her out if you want to. I just like these pics of Pride.
Oh wow! I really like that. If you post more stuff like that you'll probably peak more people's interests. I think it would be really cool to try and do a collage with everyone's horses. If not then you're free to do whatever you want with the pics I gave you. Just let me see it when you're done.