The settings for this are as Alfred said - page.searchadv.xml.config file in {root}/XMLPackage folder.
I just did this on our site and REMOVED the text in red below from page.searchadv.xml.config :-
Code:
<td align="left">
<xsl:value-of select="aspdnsf:StringResource('searchadv.aspx.5', $LocaleSetting)"/>*<input TYPE="RADIO" NAME="ShowPics" value="1" ><xsl:if test="/root/QueryString/showpics = 1"><xsl:attribute name="checked">checked</xsl:attribute></xsl:if></input>
<xsl:value-of select="aspdnsf:StringResource('searchadv.aspx.6', $LocaleSetting)"/>*<input TYPE="RADIO" NAME="ShowPics" value="0" ><xsl:if test="/root/QueryString/showpics = 0 or not(boolean(/root/QueryString/showpics))"><xsl:attribute name="checked">checked</xsl:attribute></xsl:if></input>
</td>
Then in SKIN_?/template.ascx and/or hometemplate.ascx I ADDED the following (in red) to the form section,
Code:
<form name="topsearchform" method="get" action="searchadv.aspx">
....
<input type="text" size="15" name="SearchTerm" class="searchBox" id="searchBox" autocomplete="off"
onfocus="javascript:this.style.background='#ffffff';" onblur="javascript:this.style.background='#dddddd';" />
<input TYPE="hidden" NAME="ShowPics" value="1" />
And now when people search from the search bar or from the advanced search page it defaults to showing pics.
As always, make sure to have backup copies of your source files in case you need to go back. This may not be the best solution but is tested and working for me.