“Thanks for your reply but my question is about individual pages, not the archives. “
Both the Page and Posts Featured Images are controled from the Content Archives Section in the Settings. The code added in the functions file is what activates them. If you want to turn Featured Images on or off you would use the featured Image option in the Content Archives.
Since the alignment option doesn’t seem to be working from the settings page you can add this in your CSS –
.page .featured-image {
text-align: center;
}
That should work. Here’s what it will look like when you add the code – http://i.imgur.com/JN15Rdg.png
Let me know if that helps