How can I set flickr images as thumbnails?

Hello .
First thanks all of auto blog expert here for answering users questions
Now its my turn
Please guide me how can I set flickr images as thumbnails?
Imagine Im using a theme which is supporting custom fields So I want to show flickr images as the thumbnails for posts.
EDIT: I use wp-robot !
Thanks in advanced.

Your helping will be appreciated
Please teach me.

Well, I tried to do it with myself: :ranger:
I defined custom fields with true value and name and I was playing about 3 hours witht that ! Finally I found out my theme doesnt show thumbnails from another sites and they must be in upload folder of wordpress

So please suggest me which theme can show thumbnails from another sites?
Thanks.