Komir,
I'm still playing with this myself, but to associate an image with a category, you'll need to edit the
style.css file located within your theme folder.
Starting at about line 126, you'll see
/* categories image */ ....
You'll then see many lines like this:
.home #main .categories .category h1 .category.jobs { background:......To associate a category with an image, just change ".category.jobs" to ".category.the-name-of-your-category".
Sometimes you have to add a
_1 after it, like ".category.jobs_1" to get it to work. You can know exactly what you need to use by viewing the source code in your browser.... just look for a line like, "<span class="category jobs">. If it instead says, "<span class="category jobs_1">, you'll know to add _1 (or whatever else the category might be called).
I'm still learning this all but, that works for me!
Jesse