you have to edit template forumhome like this :
{htmldoctype}
<html>
<head>
<!-- no cache headers -->
<meta http-equiv="Pragma" content="no-cache">
<meta http-equiv="no-cache">
<meta http-equiv="Expires" content="-1">
<meta http-equiv="Cache-Control" content="no-cache">
<!-- end no cache headers -->
<meta name="keywords" content="vbulletin,forum,bbs,discussion,jelsoft">
<meta name="description" content="$bbtitle is a discussion forum powered by vBulletin. To visit the forum, go to $bburl/ . To find out about vBulletin, go to http://www.vbulletin.com/ .">
<title>$bbtitle - powered by vBulletin</title>
$headinclude
</head>
<body>
$header
<!-- text -->
<table>
<tr><td><img src=HERE YOU HAVE TO PUT NAME OF IMAGE ThAT YOU WANT TO BE DISPLAYED></td><td>
<table cellpadding="2" cellspacing="0" border="0" width="{contenttablewidth}" {tableinvisibleextra} align="center">
<tr valign="bottom">
<td><img src="{imagesfolder}/vb_bullet.gif" align="middle" alt=""> <normalfont><b>$bbtitle</b></normalfont></td>
<td align="right"><smallfont>$welcometext<br><b>$newposts</b></smallfont></td>
</tr>
</table>
<br>
<table cellpadding="2" cellspacing="0" border="0" width="{contenttablewidth}" {tableinvisibleextra} align="center">
$unregwelcomemessage
<tr valign="bottom">
<td><smallfont>
Registered Members: <b>$numbermembers</b><br>
Total Threads: <b>$totalthreads</b> | Total Posts: <b>$totalposts</b><br>
Welcome to our newest member, <a href="member.php?s=$session[sessionhash]&action=getinfo&userid=$newuserid"><b>$newusername</b></a>
</smallfont></td>
<td align="right"><smallfont>
The time now is $timenow.<br>
You last visited: $bbuserinfo[lastvisitdate].
</smallfont></td>
</tr>
</table>
<!-- /text -->
<br>
<!-- main -->
<table cellpadding="{tableouterborderwidth}" cellspacing="0" border="0" bgcolor="{tablebordercolor}" {tableouterextra} width="{contenttablewidth}" align="center"><tr><td>
<table cellpadding="4" cellspacing="{tableinnerborderwidth}" border="0" {tableinnerextra} width="100%">
<tr align="center">
<td bgcolor="{tableheadbgcolor}"><smallfont> </smallfont></td>
<td bgcolor="{tableheadbgcolor}" width="80%" align="left"><smallfont color="{tableheadtextcolor}"><b>Forum</b></smallfont></td>
<td bgcolor="{tableheadbgcolor}"><smallfont color="{tableheadtextcolor}"><b>Posts</b></smallfont></td>
<td bgcolor="{tableheadbgcolor}"><smallfont color="{tableheadtextcolor}"><b>Threads</b></smallfont></td>
<td bgcolor="{tableheadbgcolor}" nowrap><smallfont color="{tableheadtextcolor}"><b>Last Post</b></smallfont></td>
</tr>
$forumbits
$loggedinusers
$pminfo
</table>
</td></tr></table></td></tr></table>
<!-- /main -->
<br>
<!-- timezone/login-->
<table cellpadding="2" cellspacing="0" border="0" width="{contenttablewidth}" {tableinvisibleextra} align="center">
<tr valign="top">
<td><smallfont>$timezone</smallfont></td>
<td align="right">$logincode</td>
</tr>
</table>
<!-- /timezone/login -->
<br>
<!-- icons -->
<table cellpadding="2" cellspacing="0" border="0" width="{contenttablewidth}" {tableinvisibleextra} align="center">
<tr>
<td align="center">
<img src="{imagesfolder}/on.gif" border="0" alt="On" align="absmiddle">
<b><smallfont>New posts</smallfont></b>
<img src="{imagesfolder}/off.gif" border="0" alt="Off" align="absmiddle">
<b><smallfont>No new posts</smallfont></b>
<img src="{imagesfolder}/lock.gif" border="0" alt="Closed Forum" align="absmiddle">
<b><smallfont>A closed forum</smallfont></b>
</td>
</tr>
</table>
<!-- /icons -->
$footer
</body>
</html>