Image
Howto - Slideshow
The slideshow is a a view. It is only visible for anonymos users on the fronpage. If you want to edit the block you have to navigate to the view itself.
Administer » Site building » Views ---> Gallery (the name of the view).
To add or delete images from the slideshow you have to administrate the image gallery 'slideshow'.
Only drupal_admin can do that.
Anonymus Users have the permission to view the content but not able to see the image gallery page itself.