Using Ctools, how do I render a managed_file from system form?
Okay, it's not my day today :D

Here's how to do what you were asking:

// Load the managed file. You need this so you can get the URI.
$file = file_load(YOUR_FILE_ID);
// Generate the output.
$output = theme('image', array(
  'alt' =&gt; t('Your image alt title'),
  'title' =&gt; t('Your image human title'),
  'attributes' =&gt; array('src' =&gt; $file-&gt;uri),
));