title: How to set background image in MacOS Mojave pkg installer using productbuild?
body: <p>I'm using <code>productbuild</code> to create a .pkg installer for MacOS Mojave. I've read the <a href="https://developer.apple.com/library/archive/documentation/DeveloperTools/Reference/DistributionDefinitionRef/Chapters/Distribution_XML_Ref.html" rel="noreferrer">schema reference for the Distribution.xml file</a>. I am successfully using this to include a custom welcome. Therefore I know my resource path is being used correctly when I run:</p>
  
  <p><code>productbuild --resources ./res --sign "$PKG_SIGN_ID" --distribution Distribution.xml foo.pkg</code></p>
  
  <p>But I can't seem to create a custom background image. I've tried various jpg and png images.</p>
  
  <p>I have read <a href="https://stackoverflow.com/questions/17576534/how-does-one-set-a-background-image-in-an-osx-pkg">this question and answer</a> and I've tried with and without a <code>en.lproj</code> subdirectory within my resources directory.</p>
  
  <p>My <code>Distribution.xml</code> ends up looking like this:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;installer-gui-script minSpecVersion="1"&gt;
  &lt;background file="background.jpg" mime-type="image/jpeg" scaling="tofit"/&gt;
  &lt;welcome file="welcome.html"/&gt;
  &lt;title&gt;My App&lt;/title&gt;
      &lt;pkg-ref id="com.foo.myapp"/&gt;
      &lt;options customize="never" require-scripts="false"/&gt;
      &lt;choices-outline&gt;
          &lt;line choice="default"&gt;
              &lt;line choice="com.foo.myapp"/&gt;
          &lt;/line&gt;
      &lt;/choices-outline&gt;
      &lt;choice id="default"/&gt;
      &lt;choice id="com.foo.myapp" visible="false"&gt;
          &lt;pkg-ref id="com.foo.myapp"/&gt;
      &lt;/choice&gt;
      &lt;pkg-ref id="com.foo.myapp" version="1.0" onConclusion="none"&gt;foo.pkg&lt;/pkg-ref&gt;
  &lt;/installer-gui-script&gt;
  </code></pre>
  
  <p>Is this no longer possible to do with Mojave?</p>