Recovery of files in iphoto
First, I would check the trash from within iPhoto to see if you can simply undelete the photos.
If that doesn't work, hopefully you have your Time Machine backup available. Go to your Photos folder in Finder, then from the Time Machine icon on your Menu Bar, select Enter Time Machine... Once active, you'll be able to find a recent copy of your iPhoto.Library package and restore it.
Good practices would also suggest that you move your existing iPhoto.Library to a safe location before you do the above  so that it is not overwritten until after you've verified the restore.