code: public static void fixImageSourceUrls(Map<String, Object> fileContents, JBakeConfiguration configuration) {
          String htmlContent = fileContents.get(Attributes.BODY).toString();
          boolean prependSiteHost = configuration.getImgPathPrependHost();
          String siteHost = configuration.getSiteHost();
          String uri = getDocumentUri(fileContents);
  
          Document document = Jsoup.parseBodyFragment(htmlContent);
          Elements allImgs = document.getElementsByTag("img");
  
          for (Element img : allImgs) {
              transformImageSource(img, uri, siteHost, prependSiteHost);
          }
  
          //Use body().html() to prevent adding <body></body> from parsed fragment.
          fileContents.put(Attributes.BODY, document.body().html());
      }
docs: Image paths are specified as w.r.t. assets folder. This function prefix site host to all img src except
  the ones that starts with http://, https://.
  <p>
  If image path starts with "./", i.e. relative to the source file, then it first replace that with output file directory and the add site host.
  
  @param fileContents  Map representing file contents
  @param configuration Configuration object