With iOS 11 Apple introduced two new formats HEVC (the High Efficiency Video Codec) and HEIF (High Efficiency Image Format) to their ecosystem.
Changes in camera technology every year makes it necessary to work on storage optimization. The photos taken from HEIF/HEVC takes 50% less space as compared to 25 years older technology JPEG, that too without loss in quality. It will also mean less bandwidth while streaming or broadcasting and more space for users with lower storage devices. Checkout the comparison: http://nokiatech.github.io/heif/comparison.html.
Many people are already taking advantage of this format with iOS 11 beta being released to public last month. This being said major Photo Sharing giants like Facebook, Flickr ,Google Photos does not support HEIF format yet. It is bad news for people who use Google Photos to backup their gallery instead of iCloud.
The product lead of google photos confirmed they are working on it replying to a tweet
We're on it
— David Lieb (@dflieb) June 30, 2017
we don’t have a timeline for this as of now but expect it to be released by the release of iOS 11.
Till then you can set your camera to use JPEG by going to Settings > Camera > Formats and set Camera Capture to “Most Compatible”. This will enable use of JPEG for photos and H.264 for videos.
Plus point to apple for not forcing this and giving a choice to choose from.