Images not showing on post pages?

My header image and a number of my sidebar images work on all the regular pages, but not on the individual posts. They were working yesterday, but today I attempted to add a ‘stumbleupon button’ to my individual posts. Now my images aren’t showing up.

I’m pretty new at all of this and am muddling my way through. I’m also pretty positive I didn’t delete any code on the page I was editing, so does anyone know what I might have done to make this happen?

My website is: https://www.mingle-mangle.net