[sualfred]

Code:

    <variable name="Fanart">
        <value condition="String.IsEqual(Container.FolderPath,videodb://movies/genres/)">http://localhost:52307/getmoviegenreimages&amp;title=$INFO[Listitem.Label]&amp;type=fanart.0</value>
        <value condition="String.IsEqual(Container.FolderPath,videodb://tvshows/genres/)">http://localhost:52307/gettvshowgenreimages&amp;title=$INFO[Listitem.Label]&amp;type=fanart.0</value>
        <value condition="[Container.Content(seasons) | Container.Content(episodes)] + !String.IsEmpty(Container.Art(tvshow.fanart))">$INFO[Container.Art(tvshow.fanart)]</value>
        <value condition="!String.IsEmpty(Container.Art(artist.fanart))">$INFO[Container.Art(artist.fanart)]</value>
        <value condition="!String.IsEmpty(ListItem.Art(fanart))">$INFO[ListItem.Art(fanart)]</value>
        <value condition="!String.IsEmpty(Window(home).Property(SkinHelper.ListItem.Art.Fanart))">$INFO[Window(Home).Property(SkinHelper.ListItem.Art.FanArt)]</value>
    </variable>

As you can see it checks first if a local artwork is available (ListITem.Art(fanart)). Only if it's empty the SkinHelper value is going to be used.
But keep in mind that SkinHelper runs as a service and will always download them. No matter if they are used or not.