Until now, in the Google suite of apps and services photos have been saved for viewing and editing in the Google Plus Photos app. Mobile devices can be configured for automated image upload to Google Plus right after capture, so your images have synced to your PC or other devices by the time you get home. Google Drive on the other hand has been the cloud space for documents, spreadsheets and other files.

With the latest update to Android, iOS and web versions of Google Drive this has changed. Photos are now also accessible in Google Drive where they can be managed and moved into folders with other file types. If you are a Google Plus Photos user there is no need to worry though as the app will continue to work as before. After the apps have been updated newly captured images will appear in drive immediately. Your existing collection will be migrated over the next few weeks. 

Source: Google Drive Blog