Unity: GetGraphicsFormat_Native_TextureFormat can only be called from the main thread

Question

I develop a plugin based on .NET 4.7 for unity and want to send images via events. This works so far. But when firing this events from another thread of my plugin library I get the error:

GetGraphicsFormat_Native_TextureFormat can only be called from the main thread.

How can I workaround this problem? My Code:

// .NET PLUGIN
public delegate void StreamHandler(MemoryStream stream);
public event StreamHandler stream;

public  void helloWorld()
{
        thread = new Thread(dowork);
        bm = new Bitmap("c://tests//3by2.jpg");
        bm2 = new Bitmap("c://tests//ar-05.jpg");
        memoryStream = new MemoryStream();
        memoryStream2 = new MemoryStream();
        bm.Save(memoryStream, System.Drawing.Imaging.ImageFormat.Jpeg);
        bm2.Save(memoryStream2, System.Drawing.Imaging.ImageFormat.Jpeg);
        thread.Start();
}

private void dowork()
{
    for (int i = 0; i < 10; i++)
    {
        this.stream(memoryStream);
        System.Threading.Thread.Sleep(100);
        this.stream(memoryStream2);
        System.Threading.Thread.Sleep(100);
    }
}


// Unity ---------------------------------------
Class1 class1 = new Class1();
class1.Log += new Class1.LogHandler(Logger);
class1.stream += new Class1.StreamHandler(streamhandle);
class1.helloWorld();

void streamhandle(MemoryStream ms)
{
     Texture2D texture = new Texture2D(128, 128);
     texture.LoadImage(ms.ToArray());
     m_RawImage= RawImage.FindObjectOfType<RawImage>();
     m_RawImage.texture = texture; 
}