Okay, what is wrong with the tail on the -17 in the foreground? It resembles a D model, but even those were more angular and the tail markings on the foreground look weird. Cool photo, but some things in it don't look right. The horizontal stab. on the a/c in the background is WAY out of proportion. The chin turrent on the first aircraft also looks off.
Chin turrents weren't intoduced until the G models, though I believe a few of the F models were retrofitted. All but certain these are 'G' model aircraft, though what series I couldn't begin to guess. The color of the top of the rudder may make the plane in the background look a bit off. The finflash 'S' is curious to me; could be a bird from the 493d BG, but there's not a lot of information available in that picture. Could also be the 34th, but the 'S' doesn't look right for that. Hard for me to tell. Somebody better read on the subject could probably figure it out. Just about has to be the ETO, though, as I don't think G-model B-17s were used in the PTO in any great numbers (mostly B-24s and -29s there, range issues) and the MTO only had six groups, all of those marked with a 'Y' looking thing on the top of of the rudder. Obviously, there were other users out there, but none I think would match up here.
It is a cool picture, though,
Honestly, the first thought I had was "Who 'shopped a He-111 tail onto a B-17?".
Side note: if anyone ever wants to walk through a B-17, Fantasy of Flight in FL has one as a static display. When you walk into it you'll see how miserable the air war was. I still think 12 O'clock High is one of the best movies ever made.