Picture come out with black dot inthe middle of the picture

If Alex's comment didn't resolve your problem, check for dust inside the camera body and on the part of the lens that goes into the camera body. The highlight indicator he speaks of will show on the LCD screen, but should not show up on your final picture once downloaded from the camera. Since the optics on that end of the lens are smaller, they are more susceptible to dust and dirt. If there is dirt or dust inside the camera body and you are not familiar with how to clean it, same yourself some headaches and take it to a qualified camera shop. You can seriously damage the interior optics of your camera by attempting to clean it the wrong way.

Like a flashing blotch? It might be the "hot spot" indicator, in which case its nothing to worry about. It just highlights hotspots in your image.