iPhone EXIF数据

我使用的是我正在拍摄的一张照片中的iPhone EXIF数据。

目前,我得到的EXIF数据是:

{
    ApertureValue = "2.970854";
    ColorSpace = 1;
    ComponentsConfiguration =     (1,2,3,);
    ExifVersion =     (2,2,1);
    ExposureMode = 0;
    ExposureProgram = 2;
    ExposureTime = "0.03333334";
    FNumber = "2.8";
    Flash = 16;
    FlashPixVersion =     (1,0);
    FocalLength = "3.85";
    ISOSpeedRatings =     (500);
    MeteringMode = 3;
    PixelXDimension = 640;
    PixelYDimension = 480;
    SceneCaptureType = 0;
    SensingMethod = 2;
    Sharpness = 2;
    ShutterSpeedValue = "4.911055";
    SubjectArea =     (319,239,230,172);
    WhiteBalance = 0;
}

如何指定要返回的新密钥? 有人知道这在iOS4.1中是如何实现的吗?