I recently upgraded an app to rails 4 from version 3.2 and noticed the images for the jQuery UI widgets were no longer showing in the production environment. They still showed up when I was in the development environment though. I did some googling and found out the reason the images are no longer showing is because Rails 4 no longer precompiles images in the assets folder.
Fortunately I found an easier solution that does not involve making any changes to the config nor to the css file.
The jQuery UI files were in the vendor assets folder, and the file structure looked like this:
/vendor /assets /stylesheets /jquery-ui /images jquery-ui.css
All I did was move the images folder from
/public /assets /jquery-ui /images
And now the jQuery UI images are showing again.