iOS: UITableView cells gets mixed up while scrolling

I am facing one issue regarding UITableView cells get mixed up while scrolling, specially for images.

I am not sure why this is going one.
I have change the patter for displaying then also its get mixed up.
Below is my code.

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *cellIdentifier = @"FriendsCell";
    FriendsTableCell *cell = [tableView dequeueReusableCellWithIdentifier:cellIdentifier];

    if (cell == nil)
    {
        NSArray *nib = [[NSBundle mainBundle] loadNibNamed:@"FriendsTableCell" owner:self options:nil];
        cell = [nib objectAtIndex:0];
    }

    return cell;
}

- (void)tableView:(UITableView *)tableView willDisplayCell:(UITableViewCell *)cell forRowAtIndexPath:(NSIndexPath *)indexPath
{
    FriendsTableCell *simpleTableCell = (FriendsTableCell *)cell;

    _model = [_contentArray objectAtIndex:indexPath.row];

    simpleTableCell.nameLabel.text = _model.fullname;

    if(_friendsSegmentControl.selectedSegmentIndex == 0) {

        simpleTableCell.followButton.hidden = NO;
        simpleTableCell.removeButton.hidden = NO;
        simpleTableCell.unBlockButton.hidden = YES;
        simpleTableCell.ignoreRequest_btn.hidden = YES;
        simpleTableCell.rejectRequest_btn.hidden = YES;
        simpleTableCell.acceptRequest_btn.hidden = YES;

        simpleTableCell.removeButton.tag = indexPath.row;
        [simpleTableCell.removeButton addTarget:self action:@selector(deleteFriend_btn:) forControlEvents:UIControlEventTouchUpInside];

        simpleTableCell.followButton.tag = indexPath.row;

        if([_model.isfollowed isEqualToString:@"YES"]) {
            [simpleTableCell.followButton setImage:[UIImage imageNamed:@"follow_yellow.png"] forState:UIControlStateNormal];
            [simpleTableCell.followButton addTarget:self action:@selector(unfollowFriend_btn:) forControlEvents:UIControlEventTouchUpInside];
        }
        else {
            [simpleTableCell.followButton setImage:[UIImage imageNamed:@"follow_white.png"] forState:UIControlStateNormal];
            [simpleTableCell.followButton addTarget:self action:@selector(followFriend_btn:) forControlEvents:UIControlEventTouchUpInside];
        }
    }

    NSString *escapedString = (NSString *)CFBridgingRelease(CFURLCreateStringByAddingPercentEscapes(NULL,(__bridge CFStringRef) _model.prof_pic,NULL,(CFStringRef)@"!*'();:@&=+$,/?%#[]",kCFStringEncodingUTF8));

    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0ul);
    dispatch_async(queue, ^(void) {

        NSData *imageData = [[NSData alloc] initWithContentsOfURL:[NSURL URLWithString:[NSString stringWithFormat:@"http://ift.tt/1QyVOl3",escapedString]]];
        UIImage *image = [UIImage imageWithData:imageData];
        dispatch_async(dispatch_get_main_queue(), ^{
            simpleTableCell.profileImageView.image = image;
        });
    });

}