[adun79]

If you want to replace it with tv show landscape or fanart for unwatched episodes, find InfoWallThumbVar in Variables.xml and add these two lines before the two <value> lines:

<value condition="String.IsEqual(ListItem.DbType,episode) + !Integer.IsGreater(ListItem.Playcount,0) + !String.IsEmpty(ListItem.Art(tvshow.landscape))">$INFO[ListItem.Art(tvshow.landscape)]</value>

<value condition="String.IsEqual(ListItem.DbType,episode) + !Integer.IsGreater(ListItem.Playcount,0) + !String.IsEmpty(ListItem.Art(fanart))">$INFO[ListItem.Art(fanart)]</value>

If you want to make it a skin option, in SkinSettings.xml, inside the block that starts with <control type="grouplist" id="600"> add this

<control type="radiobutton" id="6051">
<label>Hide thumbnails for unwatched episodes</label>
<include>DefaultSettingButton</include>
<onclick>Skin.ToggleSetting(hide_thumbs)</onclick>
<selected>Skin.HasSetting(hide_thumbs)</selected>
</control>

then in the two lines that you added to InfoWallThumbVar add the condition + Skin.HasSetting(hide_thumbs), so basically

<value condition="String.IsEqual(ListItem.DbType,episode) + Skin.HasSetting(hide_thumbs) + !Integer.IsGreater(ListItem.Playcount,0) + !String.IsEmpty(ListItem.Art(tvshow.landscape))">$INFO[ListItem.Art(tvshow.landscape)]</value>

<value condition="String.IsEqual(ListItem.DbType,episode) + Skin.HasSetting(hide_thumbs) + !Integer.IsGreater(ListItem.Playcount,0) + !String.IsEmpty(ListItem.Art(fanart))">$INFO[ListItem.Art(fanart)]</value>