UIImageViewの作成

UIImageView *imageView = [[UIImageView alloc] initWithFrame:CGRectMake(10, 10, 200, 150)];
// UIViewのプロパティ：コンテントモード
// UIViewContentModeScaleAspectFit:アスペクト比を保つ
imageView.contentMode = UIViewContentModeScaleAspectFit;
// 表示画像の設定
imageView.image = [UIImage imageNamed:@"poppy.jpg"];
// UIImageViewをviewに追加
[self.view addSubview:imageView];

UIImageView *imageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"poppy.jpg"]];
imageView.frame = self.view.frame;
imageView.contentMode = UIViewContentModeScaleAspectFit;
[self.view addSubview:imageView];