Guys why are you killing yourselves with this registry fix if there is a perfectly easy solution. You guys are on windows 10 right? Edit the image a little by lowering/increasing the brightness by one (Use the photos app as an editor). Click save a copy and then set it as lock screen. Now what it does is basically save a new fresh copy which isn't corrupt or anything. I don't know if it works on you but it worked for me.
My issue started in window 8.1, it's too bad because one of the only reasons I upgraded was in hopes that this issue would get resolved. Before today I was stuck on some random image from a Bing app I had about a year ago, but I renamed my System Data folder like outlined in one of the forms and now I just get a blank red screen for the lock screen. When I try to change my lock screen picture, it doesn't even give me an error, it just spins and spins for hours and hours!!!!
After much reading I managed to fix this problem.
I didn't have an image at the lock screen at startup. Whenever I tried to change the image to something of my preference it showed gray screen with endless loading.
Anyway, here is what I've done:
First I disabled apps that show on lockscreen:
Then I removed everything from [HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Lock Screen] , or at least remove most things from it. (The reason is the key will be populated with info later)
Or you can use this reg key with minimal entries: https://app.box.com/s/zdqvhh2cnqqth0hifw3hnb4b3v3eu0hm
After that navigate to C:\ProgramData\Microsoft\Windows
There you will find SystemData folder.
You have to take ownership of that folder. Here is a tutorial how: LINK
After that you can either rename the folder to SystemData_bak or delete it (your choise).
Finally restart explorer. Open Task Manager, find Windows Explorer and click on Restart.
And voila I was able to change the lock screen image.
You can check the reg key is now populated and SystemData is recreated.
A little background. I upgraded to Windows 10 from Windows 7 Ultimate. After the upgrade was complete, I did a Reset this PC to essentially get a fresh install of Windows 10. I was initially able to set a Lock Screen background and it was working for a few weeks. I then had a display issue when I was using RDP from work to my computer. All the fonts in Chrome were super small. I figured it was just the remote session, but when I got home it looked the same. I rebooted, same issue. I can't recall exactly what I did but it was after it had run updates. I recall uninstalling a Flash update and that seemed to fix the issue I was having, but then I noticed my Lock Screen no longer being the image I chose and started trying to fix that issue. The Lock Screen Apps do not appear on the Lock Screen as well. So at this point it may be more advantageous to just reset the PC again.
I was having the same problem, cant change the lockscreen bg image and facing with endless loading circle. First, i tried restart my computer and tried again, unlike my expectations it isnt fixed. When i searched it on the internet, figured out that it is a common problem requires sth to be done. But i didnt want to follow long steps, i felt lazy. Instead i turned off wifi and tried it again. It worked.
If your machine has group policy set to Disable "Require Cntrl Alt Del", this will cause your lock screen to not show selected image. Machine doesn't have to be on a domain as this can be set locally as well. So, I have an image, I saved it as a .png and put it in Windows\Web\LockScreen...you can put yours anywhere.
Next, do the following steps and it will fix the issue:
Go to regedt
HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\Personalization (if personalization doesn't exist, create it)
Create a new string value named LockScreenImage.
Set its value data to the full path of the desired image which will be used as the lock screen image (ex. c:\windows\web\lockscreen\imagename.png