Wallpaper won't change

[Snowhog]

Okay. Just to test, after selecting/applying the desired new wallpaper (that doesn't reflect as the active desktop wallpaper), logout and log back in. Is the desktop wallpaper now reflecting your choice?

[claydoh]

Kinda sounds like a permissions problem. Check your home folder and make sure nothing in there is owned by root

I am thinking the same thing here.
Where are the images located to begin with (drive, partition, external storage, network storage, etc)?
Maybe some screenshots would be warranted here so everyone can see how things are working, and not.

[Don]

This is an update reflecting the recent comments from Snowhog, oshunluvr, and claydoh. (1) I did log out and back in, but no change. (2) I'm the owner of everything in my home directory. (3) Partitions: /dev/nvme0n1p1: 1Mb, grub2.core.img
/dev/nvme0n1p2: EFI system partition, fat 32, /boot/efi and 513MiB space
/dev/nvme0n1p3: OS and all directories, ext4 / and 1.82TiB space
Everything is on disk storage; nothing external or network
On p3, I have /Home, of which I am the owner. The pictures I'm trying to use are /Home/Downloads/Wallpaper/Fall Pictures.

The truly weird thing is that some of the jpg images will load as desktop wallpaper and others will not. I see no pattern to it, and, as I mentioned in an earlier note, I've used all of the same images in years past with no problem. Perhaps the non-loading ones are somehow corrupted, though Gwenview shows them perfectly. As Yul Brynner said many years ago (showing my age), "Is a puzzlement."

[Snowhog]

The truly weird thing is that some of the jpg images will load as desktop wallpaper and others will not.

That could be due to the offending images not actually being the file type indicated. Just because a file has a specific extension, doesn't always mean that that is the file type it really is.

[Don]

Interesting. When I go into Dolphin/properties for each image, image type does show JPG, but I don't know whether Dolphin is merely reflecting the extension there. Is there another way I can check the true file type?

[Don]

I have checked the permissions for each image. They are all (the ones that load and the ones that don't) -rw-r--r--

[Snowhog]

You can open a Konsole in the directory where the images reside. Type: file [name of file] and press Enter. This will return the file data information. The first item will be the actual image type.

[Don]

That's a useful tip; thanks. Unfortunately (or fortunately) all the jpg files show as true jpgs on using the file command.

[Snowhog]

Hmm. Let's eliminate the possibility that it's something about your user account. Create a new login user. System Settings > Users and click on the + Add New User button. Once the new user is created, copy (as root) one of the non-displaying image files to the new users /home/[new user name]/Pictures directory. Then, logout and log in as the new user. See if the new user can change the background wallpaper to that image.

[Don]

Snowhog,
Sorry. It took me a while. I created the new account, but it turned out that the new guy didn't have any of the right files, so I had to transfer some to him. Unfortunately, same problem. I'm not sure I like this new guy; I think I'll drop him from the team.

[Snowhog]

That a new user is also experiencing this really makes me believe it is the specific image files. Something about them isn't liked by Kubuntu/Plasma.

[oshunluvr]

So you said sometimes it works and others not. Is it consistent based on the image you choose? In other words does image A always load but image B never loads?

[Don]

Snowhog, that may be right. This is happening on both my desktops. I just can't imagine what it is, since the images load perfectly in both Paint and Gwenview.
oshunluvr, it does seem to be consistent, which seems to me to point in the direction Snowhog just suggested.

Listen, I am incredibly grateful for the help everyone has offered, but I certainly did not want to take up everyone's day. The problem is strange and vexing, but hardly a big deal; it isn't going to interfere with using the machines. After all, we're talking about eye candy here. I think I should just grow up and live with it.