abstract class ZefyrImageDelegate<S> {
/// Unique key to identify camera source.
/// Unique key to identify gallery source.
/// Builds image widget for specified image [key].
/// The [key] argument contains value which was previously returned from
Widget buildImage(BuildContext context, String key);
/// Picks an image from specified [source].
/// Returns unique string key for the selected image. Returned key is stored
/// Depending on your application returned key may represent a path to
/// an image file on user's device, an HTTP link, or an identifier generated
/// by a file hosting service like AWS S3 or Google Drive.
Future<String> pickImage(S source);