Covers not showing in Explorer

Forgive me if I don't use all the right terms....I've been using the program for years. I make my own cover art for compilation albums that I put together. I use old photos or whatever, edit them and resize the. I've done the same for years. Today I added a cover to a group of files and the art is not showing on the mp3 files. Only when I open them in iTunes can I see the art. If I open them in Media Player the art is not there. If I check the "info" on a file in iTunes it shows the cover art is there but in the folders all of the files have the generic play button on them. I tried moving the folder, making a copy of the files, and nothing works. It was working yesterday. I think my PC updated last night. It's a new Windows HP PC. I update it all the time. The MP3 tag program is up to date. Even stranger, if I copy a file that I put a cover art tag on, let's say, the other day I made it and I move it to a new folder, the tag art doesn't show on the file. It disappears. I haven't changed any setting on my PC or in any programs so I'm not sure what is doing it. Any clues?

As an after thought I installed MP3 Tag on my kitchen PC and didn't have the same problem so it has to be a setting on my office PC. Since I didn't change anything I don't know what it could be.

What format have you used to save these images? Generally only jpg or png files are safe across most players. And for jpeg images make sure they are not saved in progressive style.

Thanks. They are saved as jpeg and as I said, I've done everything the same for years, same formats, etc. I save the photos 500x500 pixels 100dpi. I've saved them like that for years. The problem just started for me and only on this one PC but I can't see any settings that changed

What is the name of the picture?
It should be folder.jpg
Also, make sure that the pictures are really embedded.
Load the files and apply the filter
%_covers% MISSING
The file list should be empty afterwards. If it is not, then the displayed files do not have an embedded picture.

I've always just named them cover and have never had a problem. I fixed the issue anyway. I ran Windows repair and whatever was the issue fixed itself and they are all showing now. Like I mentioned, I figured it was some setting that got changed somehow. I installed VLC the other day and didn't like it so I uninstalled it. I'm guessing that changed something. All fixed now though. Thanks everyone.