Add EXIF metadata to a UIImage

I need to add EXIF metadata to a UIImage taken either from the camera or an album, then save the image to an album. How can I do this?

To take the photo I use:

picker.sourceType = UIImagePickerControllerSourceTypeSavedPhotosAlbum;
picker.sourceType = UIImagePickerControllerSourceTypeCamera;

but I don't k开发者_JAVA百科now how to add EXIF data.