Google has long maintained an optional link between Google Drive and Google Photos, but it appears that feature is going away. According to Google, many users find the connection between those services confusing. So, get ready for a "simplified" experience going forward.
Previously, you could choose in the Drive settings to make your photos folder visible. Thus, you could access the files uploaded to Google Photos and add new ones via Drive. You won't be able to do that anymore, though. Next month, new photos and videos added to Drive won't automatically appear in Photos. Likewise, new content uploaded to Photos won't appear in your Drive interface. If you delete items in one location, they won't disappear from the other. This has the potential to wreck some workflows for heavy Drive users.
"Starting in July, new photos and videos from Drive won’t automatically show in Photos. Similarly, new photos and videos in Photos will not be added to the Photos folder in Drive. Photos and videos you delete in Drive will not be removed from Photos. Similarly, items you delete in Photos will not be removed from Drive. This change is designed to help prevent accidental deletion of items across products."
Google notes that the Backup and Sync app will still be able to upload images to both services (they only count against your storage quota once if you use original quality). Any photos that have synced between the services prior to this change will remain in both places, too. If you really want to move photos and videos between Drive and Photos, Google will have a new option in Photos called "Upload from Drive." That lets you manually choose images in Drive to import into Photos. That's better than nothing, I suppose.