Cover art display

All of my MP3 songs that have no cover art are now displaying an album cover - the same cover for all songs.
When I right click on the cover art, all options are greyed out, so I can't remove the image.
All of these songs are selected by using the filter: %_covers% IS ""
The cover art it chose to display is one I hadn't accessed during this session, so it was completely random!
How can I get rid of this false display?

Note: I'm pretty new to using this software and editing mp3 tags, so I'll need a simple solution!

Thanks for any help!

Amazing ... please provide a screenshot of the dialog "Extended Tags...", which displays such a cover picture from one of those files.

DD.20140116.1854.CET

Could it be that the displayed file is in the folder of the files? And that you have not checked the option in Tools>Options>Tag "Don't show picture from folder"?
If you see a filename next to the picture in the tag panel, it is a file from the folder.

Yes, that was the case!. Thank you!

That is not quite right, there are two menu options available, when you have choosen to display a picture file from within the current folder.
OK, you got it, and we have learned probably a new aspect of confusion by the Mp3tag User interface.
Thank you!

DD.20140116.2121.CET