I downloaded some photos from Google Photos, only to find that they were in heic format (https://en.wikipedia.org/wiki/High_Efficiency_Image_File_Format). [When I originally wrote this blog post,] none of my linux programs know how to open that format — I needed them in jpg format. I found a utility to do the job: https://launchpad.net/~xiota/+archive/ubuntu/stuff-3
sudo add-apt-repository ppa:xiota/stuff-3
sudo apt-get install libheif-tools
sudo apt-get install libheif-examples
for f in *heic ; do heif-convert -q 90 $f ${f%.heic}.jpg ; done