Why is Thunar not creating and showing thumbnails of images?

A package called tumbler is needed for thunar to automatically generate thumbnails.

Even if you installed thumblerd you may not see thumbnails for remote storage, including MTP (new Android devices). Check your file manager's settings, e.g. for Thunar one have to set "Show thumbnails: always" (not "Only local files").

I had to "chown -R *username* ~/.thumbnails" obviously replacing username with your user name. This immediately fixed my problem.

Root was the owner of .thumbnails. I found this by opening GIMP and it gave an error that it could not gain access to .thumbnails, but, if GIMP isn’t giving you this error this may not be the solution for you.