Insert image from ActiveDirectory to list c#

First of all, I would like to ask question, do I need to insert image to Sharepoint as Image or byte[] array?

I have tried both ways to do that. In both cases it returns me System.ArgumentNullException. But value is there..

    SPUser user = web.EnsureUser(account);
    SPListItem item = items.Items.GetItemById(user.ID);

    web.AllowUnsafeUpdates = true;
    for (int i = 1; i < _propKeys.Length / 2; i++)
    {
       string val = person.Data.Where(a => a.Key == _propKeys[i, 0]).Select(a => a.Value).FirstOrDefault();

        if (_propKeys[i, 1] == "Image" && val != null)
        {
            item[_propKeys[i, 1]] = GetUserImage(acc);
        }
        else
            item[_propKeys[i, 1]] = val;

        item.Update();
     }
     web.AllowUnsafeUpdates = false;

To convert item to Image I have tried to use following code:

public static Image GetUserImage(string userName)
        {
            var directoryEntry = Values.enTry;
            var directorySearcher = new DirectorySearcher(directoryEntry);
            directorySearcher.Filter = string.Format("(&(SAMAccountName={0}))", userName);
            var user = directorySearcher.FindOne();

            var bytes = user.Properties["thumbnailPhoto"][0] as byte[];
            // I tried this byte array as well, got `NullReference` from there


            Image returnImage;
            using (var ms = new MemoryStream(bytes))
            {
                returnImage = Image.FromStream(ms);
            }
            return returnImage;
        }