Strangely the thumbnail images are display semi transparent http://fuelorder.co.uk/
I found that there is/was an issue with WordPress resizing the image causing a problem. The wrokaround was to create a specific sized image and remove image sizes from the media entry for the image. This done.. no change.. So then I tried a png instead of a jpg? Same result i.e. no change.
My last train of thought is maybe it is because it is a link..? However, looking at the NLP code removing the link looks tricky.. Any ideas?