The Slide Master view in PowerPoint is the place to go when you would like to add a logo across multiple slides. Click the View Tab, then click Slide Master. (This works in PowerPoint 2007, and PowerPoint 2010).
Once in the Slide Master View, click the slide design that you would like to manipulate. Inserting the logo (Insert tab- Picture command) onto the slide master 1st slide will send to the logo to all slides using it’s template design. In this example I added the Dominican Republic flag. I dragged it out of the way into the lower corner.
Notice the flag is on all the slides on the left side of the slide master view.