Computer
Find your photo and click on it
Click on download
Choose Full Resolution if you want the highest quality image, or choose Social Media for a smaller file
It will then ask where you want to save your file, choose location and click okay.
From iPhone
Find your photo and click on it
Choose Full Resolution or Social Media
Click VIEW, not download
The image will then open; press and hold (long press) on the image
A popup will appear — select Save to Photos

