First get the drawingCache(bitmap) of the imageView and then save the bitmap to the SDCard.
File folder = new File(Environment.getExternalStorageDirectory()+"/folder/");
if(!folder.exists()) folderAppointment.mkdirs();
try {
this.setDrawingCacheEnabled(true);
FileOutputStream fos = new FileOutputStream(new File(Environment.getExternalStorageDirectory()+"/folder/file"));
Bitmap bitmap = YOUR_IMAGE_VIEW.getDrawingCache();
bitmap.compress(CompressFormat.JPEG, 100, fos);
fos.flush();
fos.close();
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}