You might be out of luck if you do not have the originals, as you know now the 2010 was compressing the pictures.
First save the picture to hard drive and open it with something like iPhoto.
If you like the quality there we can continue.
If you do not like the quality it is the end of the road, no advanced settings will help here.
You could report the picture file size here, like is it in 500k- 1Meg, or more or less than 100k.
In second case your only option is to keep the picture size as small as possible to retain the quality (resolution).
EDIT:
If the pictures look good in original presentation then lets try this.
Do not copy paste.
Use presentation mode (full screen) and make a screenshot (press cmd+shift+4). You will get a cursor allowing you to select the picture., and once you have done that it will save it.
Now take look at that result first, and if happy then import it in to power point.