I was on here saying it was fake, and I was very confident in my judgment. I've since deleted those comments. Knowing that photo was taken near Centerville, Washington on Oct 10 at 1:09 PM, we can determine the angle of the sun was at 37 degrees. Any rainbow formed at that time would have been a low rainbow, with the top of said rainbow only extended about 5 degrees above the horizon.

It's real, and now I feel like a big, stupid bully. Sorry, OP.