XLST: Display an Image from a node reference and write it out if Tickbox is selected

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE xsl:stylesheet [ <!ENTITY nbsp "&#x00A0;"> ]>
<xsl:stylesheet
 version="1.0"
 xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
 xmlns:msxml="urn:schemas-microsoft-com:xslt"
 xmlns:umbraco.library="urn:umbraco.library" xmlns:Exslt.ExsltCommon="urn:Exslt.ExsltCommon" xmlns:Exslt.ExsltDatesAndTimes="urn:Exslt.ExsltDatesAndTimes" xmlns:Exslt.ExsltMath="urn:Exslt.ExsltMath" xmlns:Exslt.ExsltRegularExpressions="urn:Exslt.ExsltRegularExpressions" xmlns:Exslt.ExsltStrings="urn:Exslt.ExsltStrings" xmlns:Exslt.ExsltSets="urn:Exslt.ExsltSets"
 exclude-result-prefixes="msxml umbraco.library Exslt.ExsltCommon Exslt.ExsltDatesAndTimes Exslt.ExsltMath Exslt.ExsltRegularExpressions Exslt.ExsltStrings Exslt.ExsltSets ">

<xsl:output method="xml" omit-xml-declaration="yes"/>
<xsl:param name="currentPage"/>
<xsl:template match="/">
<!-- start writing XSLT -->

<!-- 1. Assign a vairiable 'isTicked' to the thickbox on the current page -->
<xsl:variable name="isTicked" select="$currentPage/showThumbnailInRightColumn"/>

<!-- 2 Get the Image that the 'thumbnail' (node number) link relates to -->
<xsl:variable name="media" select="umbraco.library:GetMedia($currentPage/thumbnailImage, 0)" />

<!-- 3 if the tick box is ticked write out the image -->
<xsl:if test="$isTicked ='1'">
 <p><xsl:value-of select="string(data [@alias='ShowThumbnailInRightColumn'])"/>
         <img src="{$media/umbracoFile}" alt="{$media/altText}" />
 </p>
</xsl:if>


</xsl:template>
    </xsl:stylesheet>