Downloads in thread and assigning in main thread

gistfile1.m

-(void)getPhotoWithThread
{
   if (self.photoDictionnaire)
   {
       dispatch_queue_t downloadQueue = dispatch_queue_create("flickr photoDowloader", NULL);
       dispatch_async(downloadQueue,
       ^{
                 self.photoView.image = [UIImage imageWithData:
                 [NSDatadataWithContentsOfURL:
                 [FlickrFetcherurlForPhoto:self.photoDictionnaireformat:FlickrPhotoFormatLarge]]];
                 dispatch_async(dispatch_get_main_queue(),
                 ^{
                            self.scrollView.contentSize = self.photoView.image.size;
                            self.photoView.frame = CGRectMake(0,0, self.photoView.image.size.width, 
                                   self.photoView.image.size.height);
                            self.title = [self.photoDictionnaireobjectForKey:FLICKR_PHOTO_TITLE];
                   });
 
        });
       dispatch_release(downloadQueue);
  }
  else
  {
      UIImage *image = [UIImage imageNamed: @"vide.png"];
      [self.photoView setImage:image];
   }
}

-(void)setPhotoDictionnaire:(NSDictionary *)photoDictionnaire
{
    _photoDictionnaire = photoDictionnaire;
    [self getPhotoWithThread];
    [self.photoView setNeedsDisplay];  // [self.photoView.image setNeedDisplay];
}