Background image appears on localhost site but not online

in line 37 of your HTML-Code you have the following declaration:

#header-background, #colophon, #site-navigation { 
  background: url('') no-repeat center center fixed;
  background-size: cover;
  -moz-background-size: cover;
  -o-background-size: cover;
  -webkit-background-size: cover; 
}

With Firebug I see, this is overwriting your CSS declaration, which states

#header-background {
   background: url("images/background-reclaimed.jpg") no-repeat fixed center center rgba(0, 0, 0, 0);
    display: inline-block;
    height: 100vh;
    max-height: 1000px;
}

If I turn off the first declaration, the picture shows up.

My first guess: Check your header.php, why this declaration puts a new background to #header-background.