different photos per individual forum and subforum

[FearlessWeeder]

I have run across websites where there is a photo on their home page, a different photo on their forum home/index page, and then different photos for each individual forum and sub forum. Granted they are far and few between but they are out there. I have seen their photos centered directly under the navigation bar but above the actual index or threads in a forum. These sites are very attractive and provide a considerable amount of visual interest.

I've also seen this played out on websites that must be selling advertising for individual boards too. In other words, if a site has 10 individual forums and 20 associated sub forums, there is a photo or ad or a paid sponsorship slot unique to each individual forum or sub forum directly underneath the navigation bar.

How does one go about adding a different jpeg to each page? Is it an advertising hack that people are using to insert different photos into each individual forum and sub forum?

If I am not describing what it is I am looking for, please help me better word my request.