Convert from a DataUrl to an Image in C# and write a file with the bytes

As @SLaks mentioned I didn't need a MemoryStream, the problem with my code was the path and the filename for further help this is the working code:

if (newItem.FieldType == FormFieldType.Signature)
{
    if (newItem.ItemValue != null)
    {
        //string completeImageName = Auth.host + "/" + li[i];
        string path;
        string filename;
        string stringName = newItem.ItemValue;

        var base64Data = Regex.Match(stringName, @"data:image/(?<type>.+?),(?<data>.+)").Groups["data"].Value;
        var binData = Convert.FromBase64String(base64Data);

        path = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments);

        //filename = Path.Combine(path, base64Data.Replace(@"/", string.Empty));

        long milliseconds = DateTime.Now.Ticks / TimeSpan.TicksPerMillisecond;
        string fileName = "Sn" + milliseconds.ToString() + ".PNG";
        filename = Path.Combine(path, fileName);

        if (!File.Exists(filename))
        {
            //using (var stream = new MemoryStream(binData))
            //{
                File.WriteAllBytes(filename, binData);
            //}
        }

        newItem.ItemValue = filename;

    }
}

App.Database.SaveReportItem(newItem);

And the image showed:

I just cleaned Mario's code and fine tuned regex:

public string SaveDataUrlToFile(string dataUrl, string savePath)
{
    var matchGroups = Regex.Match(dataUrl, @"^data:((?<type>[\w\/]+))?;base64,(?<data>.+)$").Groups;
    var base64Data = matchGroups["data"].Value;
    var binData = Convert.FromBase64String(base64Data);
    System.IO.File.WriteAllBytes(savePath, binData);
    return savePath;
}