Gun cameras on B-17's might have been a late war thing? Here's a photo of some B-17 crew members with new gun cameras in 1945:
https://www.superstock.com/asset/crew-members-rd-bomb-group-...
The B-29's and B-26's were built from the factory with gun camera fixtures in their turrets as well.
That said, I've hard a hard time finding any footage from a B17.