NMSSHSession *session = [NMSSHSession connectToHost:@"host"
                                           withUsername:@"user"];
    if (session.isConnected) {
        if (!session.isAuthorized) {
            NSArray *authTypes = [session supportedAuthenticationMethods];
        }

        NSString *privateKey = [[NSBundle mainBundle] pathForResource:@"privatekey" ofType:nil];
        [session authenticateByPublicKey:nil
                              privateKey:privateKey
                             andPassword:nil];

        if (session.isAuthorized) {
            NSLog(@"Authentication succeeded");
        }
    }

    NMSFTP *sftp = [[NMSFTP alloc] initWithSession:session];
    [sftp connect];

UIImage *image1 = [UIImage imageNamed:@"flower.jpg"];
 UIImage *image2 = [UIImage imageNamed:@"Wall.jpg"];
 UIImage *image3 = [UIImage imageNamed:@"Circle.jpg"];
 NSMutableData *data = [[NSMutableData alloc]init];
 NSMutableData *data2 = [[NSMutableData alloc]init];
 NSMutableData *data3 = [[NSMutableData alloc]init];

[data appendData:UIImagePNGRepresentation(image1)];
[data2 appendData:UIImagePNGRepresentation(image2)];
[data3 appendData:UIImagePNGRepresentation(image3)];

[sftp writeContents:data toFileAtPath:@"serverPath/filename.jpg"];
[session disconnect];