problem: non-existent images, how can i clean my galleries

I’ve just started using NGG and after some initial problems (due to rights, etc) I am now ready to start filling my galleries, but I immediately encountered this problem I can’t seem to solve.

take a look at this screenshot: http://screencast.com/t/uTAPhYZG6gX
where you see there are missing images.

in my Gallery overview it says there are 12 images: http://screencast.com/t/fi6e6PR0Kt

but when I look inside the galleries, folders, or even via a filemanager, I can only find 3: http://screencast.com/t/zbBC5IPrh

It’s likely these 9 “ghost” images where images which were uploaded unsuccessfully when the configuration (rights) were still wrong.

But how do I now get rid of them, they are nowhere!

https://wordpress.org/plugins/nextgen-gallery/

here’s a link to the website, the problem already appears on the homepage: http://www.sporck.eu/