adding different image to top of every page under header

So I’ve been googling my fingers raw for days trying to find the answer to this one, but have had no luck.

I’m wanting to customize my WordPress blog by adding a unique image that spans across the whole width of the page to the top of each new WP page. (The image itself wouldn’t be that wide, but I’d add a background color that would go across the page.) This image would appear just under the header at the top of each page, and would serve to announce the nature of the content on the individual pages (sort of as a subheading).

So it would look something like:

THIS IS THE HEADER
home | about | navigation stuff |

— *here is the image, unique to every page* ——————

page content

Am I right in thinking that I need to customize the template itself? Will this require php coding? Are there any online resources that I can look at? Examples where this has been done? Bueller? Bueller?

I would appreciate it if you could talk to me like I’m an idiot so that I’m sure to understand the answer. While I do have some CSS knowledge, I have no php coding knowledge and am feeling a bit disoriented in this new environment.

Sincere thanks to anyone willing to give me some advice.