Here are the modifications I did to correct the problem:
public class testEmguCV : MonoBehaviour
{
private Capture capture;
void Start()
{
capture = new Capture();
}
void Update()
{
Image<Gray, Byte> currentFrame = capture.QueryGrayFrame();
Bitmap bitmapCurrentFrame = currentFrame.ToBitmap();
MemoryStream m = new MemoryStream();
bitmapCurrentFrame.Save(m, bitmapCurrentFrame.RawFormat);
Texture2D camera = new Texture2D(400, 400);
if (currentFrame != null)
{
camera.LoadImage(m.ToArray());
renderer.material.mainTexture = camera;
}
}
}