Lightbox not working on images I add to Advanced Poll

Hi,
I needed a poll to vote on pictures, so I chose Advanced Poll module.
In choices I added html for images together with link to the picture and attributes for lightbox ... this is the code:

<a title="picture" rel="lightbox" href="/sites/default/files/pic.jpg" class="lightbox-processed">
<img  class="image image-big image-center" src="/sites/default/files/pic.jpg" title="picture"/>
</a>

This same code is used around the web and lightbox is working. I don't understand why it is not working in Advanced Poll. The picture opens in window and not in lightbox.

Do you have any similar experience. I will really apreciate your help.
Thank you