Items that are shared with the group that your Gallery is configured to use will show up on that page. I believe by default there is a group called "Gallery" that is configured to use. The site admin can change that setting from the Organization page. From the Organization page, select Edit Settings and then click the Gallery tab along the side. You can see and configure which group the Gallery uses from there.
Just unshare items with the group the Gallery uses and they should disappear from listing.
Leon
