C# camera snapshot

Question

Hi! Sorry for my english. Im a beginner in C#. I downloaded a directshow example called DXsnap from the internet. It can make a snapshot from my USB camera, but the problem is with the speed. It takes a long time to make a picture. So i decided to make  snapshot, from the preview window. The preview from the camera is placed on my form. I made procedure what makes a snapshot from the screen - something like Printscreen. When i open the captured Image, instead of the captured frame is there only a black picture. Then i tried only press the Print screen button, and the same thing happened. Have someone met this problem. Is there any solution for?