title: How image_tag is overrided and a reason to not add fingerprint
body: <p>I have rails application, with sass less and many gems.</p>
  
  <p>I try to find where <strong>image_tag</strong> is overwrited to debug why it do not add <strong>fingerprint</strong> hash to url.</p>
  
  <p>I have done <code>rails assets:precompile</code> and files with hash fingerprint are existing in public dir.
  The problem is on production and in development which I configured (as in production) like this:</p>
  
  <pre class="lang-rb prettyprint-override"><code>config.assets.compile = true
  config.assets.digest = true
  </code></pre>
  
  <p>I tried to search in <code>~/.gem/gems</code> and <code>~/.gem/bundler/gems/</code> and in project folder for <code>def image_tag</code> and <code>:image_tag</code> - no results except place where it is actually defined (<code>actionview-5.0.7.2/lib/action_view/helpers/asset_tag_helper.rb</code>).</p>
  
  <p>I tried to print some from <code>image_tag</code> at <code>asset_tag_helper.rb</code> - no any output, however at <code>asset_path</code> in <code>asset_url_helper.rb</code> output is present but no any image files processed.</p>
  
  <p>Same time <code>image_tag</code> works correct and generate correct tag with options like <code>:size</code> and so on. But do not contain a hash fingerprint</p>