Blue UFO snapped over Yellowstone River, Montana

On August 15, 2015, during sunset, a man was fishing in Yellowstone River (Montana). He took photo of beautiful sky. Later, he noticed a mysterious object in both pictures.

Witness statement:

I was out fishing in the Yellowstone River one evening when the pictures were taken.It was around 7:30 or 8:00 p.m. and I took a few of the sun behind the clouds but something kept grabbing my attention about that particular area.I kept feeling like I needed to take more pictures towards that direction. I noticed the object in one picture moving towards the cloud, and when looking at the picture before, I noticed it in the trees across the river from me. It has a strange green glow. I can't say what it was but I definitely believe that it's possibly a u.f.o. and I wanted experts to have a look.