If you own a modern age phone it’s very likely that it will store the photos you take in a wonderful format called HEIC – or “High Efficiency Image File Format (HEIF)”.
So HEIC does not quite fit yet. But you can make it fit with this on Linux.
Imagemagick and current GIMP installations apparently still don’t come pre-compiled with HEIF support. But you can install a tool to easily convert an HEIC image into a JPG file on the command line.
apt install libheif-examples
and then the tool heif-convert is your friend.