1) Assembler can add the chart image file as a file attachment - either attached to the document as a whole, or to a specific page.
<?xml version="1.0" encoding="UTF-8"?>
<DDX xmlns="http://ns.adobe.com/DDX/1.0/">
<PDF result="outDoc.pdf" >
<PDF source="inDoc.pdf"/>
<FileAttachments source="chart.jpg" nameKey="Chart">
<File filename="chart.jpg" mimetype="image/jpeg"/>
<FilenameEncoding encoding="UTF-8" />
<Description>Chart from ColdFusion</Description>
</FileAttachments>
</PDF>
</DDX>
2) If PDF Generations service is available, then the image can be converted to a PDF and then any of the pagecontent elements can be used to place the image within the PDF:
<?xml version="1.0" encoding="UTF-8"?>
<DDX xmlns="http://ns.adobe.com/DDX/1.0/">
<PDF result="outDoc.pdf" >
<PDF source="inDoc.pdf"/>
<BlankPage>
<PageOverlay>
<PDF source="chart.pdf"/>
</PageOverlay>
</BlankPage>
</PDF>
</DDX>
Note: in the most recent release, LC ES Update 1, if the source idp.document mapped to chart.pdf for the <PDF> element is not a PDF document, Assembler will attempt to call the PDFG service to convert the document to a PDF before throwing an exception. Although, I would probably change the extension of the filename to be indicative of the type of incoming content, e.g. chart.jpg or chart.gif...