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
.