More and more presentations are given on plasma/LCD screens with a wide aspect ratio. Most PowerPoint presentations are designed for a narrow 4:3 ratio (a traditional computer monitor). Most of the time, the screen will automatically stretch you image to create a bigger picture. I never understand this habit: the distorted proportions look horrible. (Judging by my own experience, this is how most people watch TV nowadays as well).
My advise: set the screen back to the narrow aspect ratio. Doing this on your computer is often tricky, the best way is to take the remote control of the screen and fix it there. A smaller picture is much better than a distorted picture.
The painting is Manet's Portrait of Irma Brunner.