If I understood correctly, you have inserted an image into the PAGE_CONTAINER template and you do NOT want it to be shown in threads?
If so... wrap the image code in a conditional, like this:
Code:
<xen:if is="{$contentTemplate} != 'thread_view'">
<img src="http://www.valvetime.net/styles/valvetime/xenforo/valve.png" />
</xen:if>