Custom image

You mean custom images in the forum-overview for example? You can already modify them via CSS because you can select them via an CSS-ID.

For the category-title in the overview with the ID 144 you can use:
#forum-category-114

Same with forums: You can select a forum with the ID 368 with:
#forum-368

Hi

Is it this part of the forum and how do i do that,im not a coder?

}

/* OVERVIEW/FORUM */
#af-wrapper .forum [class^=”dashicons-“],
#af-wrapper .forum [class*=” dashicons-“],
#af-wrapper .thread [class^=”dashicons-“],
#af-wrapper .thread [class*=” dashicons-“] {
padding: 0;
}

You can try something like this to set a image called “paper.gif” as the background:

#forum-category-114 {
    background-image: url("paper.gif");
}

#forum-368 {
    background-image: url("paper.gif");
}

And yes, the code you provided is a part of it. It is used for the icons.