Im currently building my personal blog/theme in a freshly installed WordPress 4.0 envirement. I have been banging my head on why the featured image option wasn’t visible.
Many people blame old plugins for the breakdown of the featured image, but i had a fresh install and a empty theme template… HOW HOW HOW?!!!
Here’s my solution
open functions.php of your chosen template and add the following line somewhere between the PHP tags:
add_theme_support( 'post-thumbnails' );