Use Less Space for Photos
Are you always out of space on your iPhone and in iCloud? The new iOS 11 photo format will help you get by with less storage space without sacrificing quality.
The new iOS 11 file format is HEIF and it delivers a major space saving. You need to make sure it is turned on.
Go to Settings -> Camera -> Formats and choose High Efficiency.
If you are on a PC for your computer, this may not be completely compatible, so you may want to go with Most Compatible.