A lot of people are complaining that their images stored in Google Drive are not appearing in Google+ Photos.
Google already indicates that some images like screenshots and thumbnails are not going to be visible in Google+.
Based on user feedback, it looks like Google is using EXIF information to decide whether an image should appear in Google+ Photos or not.
So, if you clean up EXIF data (more specifically date) on your photos before uploading them on Google Drive, you might not find them in your Google+ account at all.
This is kind of absurd. The integration is there. Why restrict it?
Google is also creating data based mini albums from photos in a single Google Drive folder. This is again creating a lot of nuisance for the users as their photos from one folder are scattered across multiple albums in Google+.