This is not support more of a how-to: Twenty elven Child Themes.
I have created three different solutions for enhancing the Category Page:
The first Child Theme Solution is pulling the header from the oldest post with one assigned.
Second Child Theme Solution, we can upload headers to appearance headers, the image having the same name as the category slug, when the category page is dispalyed it will use the header of the same name.
Last is a mixture of several bits, up-load headers, custom post types for Category Description which shows above the list view, selection of content output via dropdown box, and reverse sorting.
All the code is in child themes so not many files to look at, it might help some people along!
Here is a post for the third it has a download and links to one and two.