Add to xsl:stylesheet tag:
xmlns:ddwrt="http://schemas.microsoft.com/WebParts/v2/DataView/runtime"
Then add this template to be called later:
<xsl:template name="OuterTemplate.IsNew">
<xsl:param name="ModifiedValue"/>
<xsl:if test="((ddwrt:FormatDateTime(string(ddwrt:Today()), 1033, 'yyyyMMdd')) - (ddwrt:FormatDateTime(string($ModifiedValue), 1033, 'yyyyMMdd'))) < 5" >
<xsl:value-of select="string('<img src="/_layouts/1033/images/new.gif" alt="New" />')"/>
</xsl:if >
</xsl:template>
Example of using the template:
<xsl:variable name="NewIcon">
<xsl:call-template name="OuterTemplate.IsNew">
<xsl:with-param name="ModifiedValue" select="@Modified"/>
</xsl:call-template>
</xsl:variable>
<xsl:value-of disable-output-escaping="yes" select="$NewIcon"/>