Image not displaying in PDF

I have a rtf that contains an image. The image shows correctly when I view the record using a record summary. However if I use the export as PDF link the image shows as a blank box. There is also a signature field that does show correctly. If I use the print button and print to a PDF using PDF Creator the image shows correctly.

Is there anything special that needs to be done for an image to show using the built in PDF? Such as publishing the underlying report or form?