Storing cover images in the codex

I am building a virtual 78rpm collection and include with each mp3 file an image of the record label. If the song I have was downloaded from YouTube it likely has some other image as part of the Codex when I download it. I have a folder with the label image I want in the Codex. Is there a way to change the cover image by selecting my own image. I thought it would be to simply add my image into the Cover box and click save tag. However when i return to my library it still has the YouTube image. Even with my image appearing in MP3TAG cover box, if I double click the filename and plat the song with VLC Media Player, it's the YouTube image that appears. Is there a solution?

see e.g. this thread: