ImageSource From Local Resource

private byte[] ConvertImageSourceToByteArray.cs

//How to use
var imageAsByteArray = GetImageFromFile("Folder.Imagename.jpg");
var imageToBase64String = Convert.ToBase64String(imageAsByteArray, 0, imageAsByteArray.Length);

//Loading into a Xamarin Forms Image Source
theImage.Source = ImageSource.FromStream(() => new MemoryStream(imageAsByteArray));

private byte[] GetImageFromFile(string fileName)
{
    var applicationTypeInfo = Application.Current.GetType().GetTypeInfo();

    byte[] buffer = null;

    using (var stream = applicationTypeInfo.Assembly.GetManifestResourceStream($"{applicationTypeInfo.Namespace}.{fileName}"))
    {
        if (stream != null)
        {
            long length = stream.Length;
            buffer = new byte[length];
            stream.Read(buffer, 0, (int)length);
        }
    }

    return buffer;
}