you can try to this , then you get a bitmap of selected image and then you can easily find it's native path from Device Default Gallery.
Bitmap roughBitmap= null;
try {
// Works with content://, file://, or android.resource:// URIs
InputStream inputStream =
getContentResolver().openInputStream(uri);
roughBitmap= BitmapFactory.decodeStream(inputStream);
// calc exact destination size
Matrix m = new Matrix();
RectF inRect = new RectF(0, 0, roughBitmap.Width, roughBitmap.Height);
RectF outRect = new RectF(0, 0, dstWidth, dstHeight);
m.SetRectToRect(inRect, outRect, Matrix.ScaleToFit.Center);
float[] values = new float[9];
m.GetValues(values);
// resize bitmap if needed
Bitmap resizedBitmap = Bitmap.CreateScaledBitmap(roughBitmap, (int) (roughBitmap.Width * values[0]), (int) (roughBitmap.Height * values[4]), true);
string name = "IMG_" + new Java.Text.SimpleDateFormat("yyyyMMdd_HHmmss").Format(new Java.Util.Date()) + ".png";
var sdCardPath= Environment.GetExternalStoragePublicDirectory("DCIM").AbsolutePath;
Java.IO.File file = new Java.IO.File(sdCardPath);
if (!file.Exists())
{
file.Mkdir();
}
var filePath = System.IO.Path.Combine(sdCardPath, name);
} catch (FileNotFoundException e) {
// Inform the user that things have gone horribly wrong
}