Imported 32GB of images into iPhoto, 65GB library is the result - Huh?
First thing to know : There is no possibility to reduce the size of an iPhoto library without corrupting it. 

What you can do is explore your iPhoto library in ~/Picture/iPhoto Library => right click => show package content. 

In this directory you'll see multiple directories : 


Masters : holds in the original of your pictures
Preview : holds in a low resolution preview of your pictures
Thumbnails : holds in thumbnails like the ones used on faces. 


These 3 directories are the main reason of the weight of your library. The other files/directories are way lighter.