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)”.
Now the issue with this format is that your average toolchain is based upon things like Portable Network Graphics (PNG), JPEG and maybe GIF or Scalable Vevtor Graphics (SVG).
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.