title: iOS SDK posting a link & displaying a thumbnail
body: <p>I've managed to get the Facebook iOS SDK implemented into my project quite nicely with the assistance of the provided FB documentation.</p>
  
  <p>My app's FB integration is quite simple: A Facebook share button, which allows a user to post a link to their FB wall with a user-supplied comment.  Nothing earth-shattering or ground breaking.</p>
  
  <p>However, I would like to go one step further.  I don't have a thumbnail to display for the link (i.e. my own image URL), but I would like the thumbnail to be automatically selected by Facebook.</p>
  
  <p>Similar to how, from Facebook in a web browser, if you choose to Share a link from CNN.com, Facebook will automatically select thumbnails for the desired page to be shared, AND it even gives you the option to checkbox "no thumbnail".</p>
  
  <p>From the iOS dialog to share the link, I would like the thumbnail to automatically be selected (presumably it's generated from the link that you're trying to share, i.e. FB just grabs images from the page).</p>
  
  <p>Is this possible?  Again, I do not want to display "picture" with a supplied image URL in the 'attachment' NSDictionary below because I won't have the image URL.  I just want to display a hyperlink and have FB post the link on the user's wall with their comment and have FB supply the thumbnail image (similar to how it would if you posted from a web browser).</p>
  
  <p>Basically the code from Stack Overflow is:</p>
  
  <pre><code>SBJSON *jsonWriter = [[SBJSON new] autorelease];
  
  NSDictionary* actionLinks = [NSArray arrayWithObjects:[NSDictionary     
  dictionaryWithObjectsAndKeys: @"Always Running", @"text", @"http://itsti.me/", @"href", 
  nil], nil];
  
  NSString *actionLinksStr = [jsonWriter stringWithObject:actionLinks];
  NSDictionary* attachment = [NSDictionary dictionaryWithObjectsAndKeys:
                             @"a long run", @"name",
                             @"The Facebook Running app", @"caption",
                             @"it is fun", @"description",
                             @"http://itsti.me/", @"href", nil];
  
  NSString *attachmentStr = [jsonWriter stringWithObject:attachment];
  NSMutableDictionary* params = [NSMutableDictionary dictionaryWithObjectsAndKeys:
                               @"Share on Facebook",  @"user_message_prompt",
                               actionLinksStr, @"action_links",
                               attachmentStr, @"attachment",
                               nil];
  
  [_facebook dialog:@"stream.publish" andParams:params andDelegate:self];
  </code></pre>