Create new category, remember it's ID.
(In changes below replace all XX with your category ID)
"Top 10": In top.php find:
$cat_id_sql = get_auth_cat_sql("auth_viewcat", "NOTIN");
Insert below:$cat_id_sql .= ", XX";
"New images": In index.php find:
WHERE i.image_active = 1 AND c.cat_id = i.cat_id AND i.cat_id NOT IN (".get_auth_cat_sql("auth_viewcat", "NOTIN").")
Replace with:
WHERE i.image_active = 1 AND c.cat_id = i.cat_id AND i.cat_id NOT IN (".get_auth_cat_sql("auth_viewcat", "NOTIN").", XX)
"Random image": In includes/functions.php find:
$cat_id_sql = get_auth_cat_sql("auth_viewcat", "NOTIN");
Insert below:
$cat_id_sql .= ", XX";