The problem is that the image is on the overlay. When video acceleration is used the image is sent directly to the video card with only a section of the screen (marked by the color of your media player's blank screen) that shows what is on the overlay. This means that you can't use Print Screen to take a picture of the video. To deal with this problem either turn off video acceleration or else use
BS Player's screen capture function. I don't watch anime with BS Player, but I do use it for screeshots.