BlockExample.m

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    
    ...code to dequeue and setup a UITableViewCell removed...

    //retrieve our Core Data representation of the photo
    Photo* photo = [Photo photoWithFlickrData:pictObj inManagedObjectContext:context];
    if (photo.thumbnail) {
        cell.imageView.image = [UIImage imageWithData:photo.thumbnail];
    }
    else {
        //Photo objects uses Grand Central Dispatch to make a request to 
        //Flickr servers for photo downloads.
        [photo thumbnailWithBlock:^(NSData* image) {
            cell.imageView.image = [UIImage imageWithData:image];
            [tableView reloadRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationNone];
        }];
    }

    return cell;
}