A simple google of "B-17 4x-xxxxx" would be a good starting point.The tail number most likely will be missing the number 4 and more than likely followed by a 2,3,4,or 5. Narrow down air force(IE; 8th,15th) and bomb group.
There are many bomb group sites out there with search able data bases by SN,plane name, aircrew names,etc.
Many aircrews did not routinely flew the same AC, but rotated through them, so the AC in the photo may or may not have been the AC on his final mission. Once you have a little info though, you should be able to dig up quite a bit for free.
If you know the date his ship went down, try searching MACR's (Missing Air Crew Reports) for that date...A good start would be at armyairforces.com