Do you have any details of your great uncle's service career (e.g. units/bases assigned to and dates)?
To my uneducated eye, the subject B-17 looks to be in a Stateside training unit. I can confirm it's a B-17G. There's a silver B-29 behind it and a B-25 at the left of the image. Again, these types didn't often fly from the same airfields when deployed on operations which suggests, to me, that it's a Stateside location.