Upload the logo file in a File Area, get a permalink and use this code inside the footer in the Package.
 

<span class="copyright">Powered by
  <a href="LINK-to-DOMAIN_here" target="_blank">
     <img src="permalink_here" title="Company name" alt="Company name"> 
  </a>
</span>


NOTE: This snippet is provided as is, with no express or implied warranty for accuracy or accessibility.