However, if you are distributing the presentation in other forms, a higher resolution might be appropriate. A computer screen shows 96 pixels per inch, so you do not need higher resolution than that if you are only showing your presentation on-screen. This roughly translates to dots per inch (dpi) on a printout. Picture resolution is measured in PowerPoint in pixels per inch, or ppi. It does so by reducing the picture resolution to the amount needed for the type of output you specify (Print, Screen, or E-mail).
The Compress feature for pictures offers an image compression utility that reduces the size of all inserted pictures in the presentation in a single step.
By default, PowerPoint simply copies your inserted pictures into your presentation leaving the size and format largely unchanged. Although using pictures enhances the look of your presentation, it can also phenomenally increase the size of your presentation file.
