Please do the following:
- Open the presentation
- Main menu -> View -> Master -> View Master
- Choose second or master slide at the left column
- Click right mouse button on the slide background
- Choose “Background” – Click on the down arrow in the new pop up window
- Select “Fill Effects” in that menu
- Choose “Picture” tab and click “Select Picture”
- Browse, choose and apply the background
- Main menu -> View -> Normal