Usage of set Receipt From Image is Ambiguous

Hello,

I'm trying to use the set receipt from image API call and I can't figure out how to actually send you guys the image! I played around enough for it to tell me that there was an invalid base-64 encoded receipt! The issue is any reasonable image will be way too long when encoded into base-64 to be able to send over a get request. Any workaround for this?

Thanks,
Joe