uses NetEncoding,PNGImage;


procedure TForm1.FormCreate(Sender: TObject);
var
  LInputStream: TFileStream;
  LOutputStream: TMemoryStream;
  Png: TPNGImage;
begin
  LInputStream := TFileStream.Create('C:\Temp\PlateImage.txt', fmOpenRead or fmShareDenyWrite);
  try
    LOutputStream := TMemoryStream.Create;
    try
      TNetEncoding.Base64.Decode(LInputStream, LOutputStream);
      ShowMessage(LOutputStream.Size.ToString);
      LOutputStream.Position := 0;
      Png := TPNGImage.Create;
      try
        Png.LoadFromStream(LOutputStream);
        Image1.Picture.Assign(Png);
      finally
        Png.Free;
      end;
    finally
      LOutputStream.Free;
    end;
  finally
    LInputStream.Free;
  end;
end;