Is there a way to turn off the auto rotate feature for photo thumbnails in Windows 8 desktop? Would like to be able to adjust them manually.

1) Are you using photo app to view photos?

2) Do you remember making any changes prior to this?

If you are using Photo app, I would suggest you to refer to the article given below.

What to do if you have problems with an app

http://windows.microsoft.com/en-IN/windows-8/what-troubleshoot-problems-app

Also refer to the article given below.

Photos app for Windows: FAQ

http://windows.microsoft.com/en-IN/windows-8/photos-app-faq

Perform steps mentioned below and see if it helps.

a: Right click on an empty space on the desktop and click Personalize.

b: Then uncheck the option Allow the screen to Auto-rotate.

c: Then click Apply and then ok.

This is not actually a feature, but File Explorer finally respecting the rotation tag on JPEG files. You must fix the rotation yourself using an app like Photo Gallery, which comes with Windows Essentials.