Random image block and galleries privileges

Hi.
I have a problem with Random Image block.
I have three gallery, but only two of them can be viewed by anonymous users. The third gallery can be viewed only by authenticated users.
The random imagen block shows random images from all galleries, without take care with gallery permission, and then, anonymous users can see images from the third private gallery.
How can I change this?
Why Random Image block doesn't take images only from the correct galleries?
Thanks in advance.