I found this on launchpad and it answered my question. Thanks for the hilp.
I am not completely sure where these files are coming from, but http://www.aypcservices.com/?p=5525 (middle part of the page) indicates that they might be reconstructed picture files from the PhotoRec program (part of the testdisk package).
It seems they have been created in a way that they are owend by 'root', and you do not have access rights to look at them. To overcome that restriction you can do the following:
Open a terminal (Applications -> Accessories -> Terminal, or press ALT+F2, or press Ctrl+Alt+T) and in the window that opens enter "gksudo nautilus" (without the quotes). This will ask for your password and open a new file browser window with access rights as if logged in as root.
Now you should be able to browse all files.
Please use extreme caution when using this technique, because in that window the restrictions imposed on a 'normal user' (like: no rights to delete important system files) are temporarily overridden.