ulong overlayHandle = 0;
EVRInitError eError = EVRInitError.None;

OpenVRInterop.GetGenericInterface(OpenVR.IVROverlay_Version, ref eError);
CVRSystem system = OpenVR.Init(ref eError, EVRApplicationType.VRApplication_Overlay);

CVROverlay overlay = OpenVR.Overlay;
overlay.CreateOverlay("textureOverlay", "Picture Overlay", ref overlayHandle);
overlay.SetOverlayFromFile(overlayHandle, OverlayPath);
overlay.ShowOverlay(overlayHandle);