The header image is displayed if it is set in the general options. It can be hidden from specific pages and posts by using the Plus theme’s meta options.
Its visibility can be further tweaked with custom CSS if desired – the CSS depends on the site section it should apply on:
<section identifier> #header-image-main {
display: none;
}
Keep in mind that in Roseta the header image section also holds the page/post/section title and the breadcrumbs. These would no longer be visible when the header image is hidden this way.