Ok, I gave it another try with both options.
I added two pictures and added a title, description and so on to both of them. Now I created two posts (Option A and Option B). For Bption A i added one picture with some fancy guys as post thumbnail. For option B i added the other picture in the Post Header Image field.
Have a look at Jaegers.Net and scroll to January 1st to see the results. Both pictures are visible but no kind of picture description or caption, only for them, which are addid directly to the post content.