How to import photos to keynote IPAD
You can't import photos directly from Facebook in Keynote for iOS, but you can add photos from your Camera Roll. And the Facebook app for iOS lets you save photos to your Camera Roll -- open the photo in Facebook, then select 'Save Photo' from the top right menu. 

You have to repeat this process for each photo you want to include in the presentation, but it's the only way I can think of.