Not sure if this is the right place to ask this, or if I should ask in the art section.

I have figured out how to change the image of the horse if I want to, but I was wondering if there was a way to upload your own image to use as a background behind the normal horse avatars? Like if I had a photo of a field or something that I really liked and wanted to have my horses standing in, but didn't want to try to make a complete custom horse image?

Yep! This is doable. So you would have to first set your horse's background to transparent. After that, save the horse image to your device. Next, upload the image (still with a transparent background) onto the image you would like to have set as your horse background. From there, resize the image and set it as your horse's avatar

Okay, from you answer I am guessing there is not a way to load an image and set just that image as the default background for all of your horses, you have to take the horse image and make a completely new image using the default art and the custom background and load it up as an individual avatar for a single horse.

That is correct