Access to thumbnail picture not protected

[stegherr]

1. I have a data that have restricted access to only one group of people, for instance Altona 2000 seismic survey,
2. A thumbnail is associated to that data and as I'm part of the group I can see a bigger picture by clicking on the thumbnail,
3. You're not part of the group that has access to the data, but if I send you the picture address ​http://wagcoe.ivec.org/geonetwork/srv/en/graphover.show?id=38&fname=Altona_Survey_800.jpg&access=public you can see something that is actually protected,
4. In my opinion only the people part of the Geonetwork group should be able to see the picture.