Image not displayed on pdf export

I included an image in my report page . It loads on print export but not on pdf.public function pageDataRendering(&$header)
{
$header = “”;
}this displays my image but when i export to pdf i get broken image with this error msg.
Image not found or type unknown

Note that Page_DataRendering is not fired during export (assume it is a table, not report), you may customize the export class, see Customize Export Class.

What I want to do is add a logo at the top of my report page.

You may override the exportTableHeader() method as described in Customize Export Class.