title: three.js set background image
body: <p>How to create a static background image?</p>
  
  <p>For default background:</p>
  
  <pre><code>scene = new THREE.Scene();
  
  // ...
  
  renderer = new THREE.WebGLRenderer( { antialias: false } );
  renderer.setClearColor( scene.fog.color, 1 );
  </code></pre>
  
  <p>How to set a image for <code>scene.fog</code>, or set opacity for <code>clearcolor</code>?</p>