Just to confirm the therms used.
DPI: Dot’s per inch. The number of dots in a printed inch. The more dot’s the higher the quality of the print (more sharpness and detail).
PPI: Pixels per inch. Most commonly used to describe the pixel density of a screen (computer monitor, smart phone, etc…) but can also refer to the pixel density of a digital image.
Resolution: Resolution is the measure of pixels in the display, usually expressed in measurements of width x height. For example a monitor that is 1920 x 1080 is 1920 pixels across and 1080 pixels down.
Higher resolution means more detail. Higher DPI means higher resolution. Resolution is not “size”, but it’s often confused with it because higher resolution images are often bigger, but that doesn’t necessarily have to be the case.
Now to your question:
Insert a high resolution image in Power Point.
Right Click and select Format Picture ->size.
In this screen select the Resolution.
If you now click on the Compress in PP menu bar you can compress the file if you want to reduce the DPI.
If you want to export Pictures from PP2011 that you already have, than the highest resolution is equal to the original as saved, means PP would have reduced its size/resolution. Not so if you are making new presentation and save the picture in it its original size/resolution.