You can also add an Image to the Media Gallery by intent, have a look at the example code to see how it is done:
ContentValues image = new ContentValues();
image.put(Images.Media.TITLE, imageTitle);
image.put(Images.Media.DISPLAY_NAME, imageDisplayName);
image.put(Images.Media.DESCRIPTION, imageDescription);
image.put(Images.Media.DATE_ADDED, dateTaken);
image.put(Images.Media.DATE_TAKEN, dateTaken);
image.put(Images.Media.DATE_MODIFIED, dateTaken);
image.put(Images.Media.MIME_TYPE, "image/png");
image.put(Images.Media.ORIENTATION, 0);
File parent = imageFile.getParentFile();
String path = parent.toString().toLowerCase();
String name = parent.getName().toLowerCase();
image.put(Images.ImageColumns.BUCKET_ID, path.hashCode());
image.put(Images.ImageColumns.BUCKET_DISPLAY_NAME, name);
image.put(Images.Media.SIZE, imageFile.length());
image.put(DATA_CONSTANT, imageFile.getAbsolutePath());
Uri result = context.getContentResolver().insert(MediaStore.Images.Media.EXTERNAL_CONTENT_URI, image);