Tom,
When I add the image through gp hook using “if single …” php code, the header shows up in all single post. However, there is another issue, where the featured image shows up right on top of the title for every post. It looks really awkward since this image is there inside he content anyway. So I used the disable elements in each post to remove the post image/header and this removes the post image on top of title like I wanted, but also removes the header. So the only solution go each post and add the header (page header option). This doesn’t sound like an effective method. If I have 1000 single posts, it is going to be difficult to add the same header in for each post