It seems like whenever there is a PDf on a post then autonav does not take the image but rather the PDF.
For example on http://www.award-certificates.com/
you can see that there is a post showing as having a missing image. On the post that has a missing image there are 8 images that have been uploaded via WP and should show.
The same thing happens on http://www.award-certificates.com/certificates-for-kids/
I thought that I could overcome this by adding more images to the top of the post but it does not help.