For local conversion, this worked for me in Debian. Just downloaded the static build, ran the example conversion command, everything worked:

https://github.com/monostream/tifig

Another long term fix is to consider using https://heiconvert.com to easily convert your HEIC images to a more compatible format, making them accessible in your default Image Viewer on Ubuntu. It's a quick solution for hassle-free image viewing.

This heic combined still + video burst file opened in mpv

In recent Ubuntu versions (>= 18.04):

sudo apt-get install libheif-examples

And then

for file in *.heic; do heif-convert $file ${file/%.heic/.jpg}; done

In older Ubuntu or Mint versions, first add this PPA and then do the above steps.

sudo add-apt-repository ppa:strukturag/libheif
sudo apt-get update

IIRC they’re Apple’s implementation of high quality images? I just converted them to JPEG, but a quick google search has pointed me to this tool: heif-gdk-pixbuf Now I’ve not used this so cannot confirm if it’s any good, but it might be worth checking out.

HEIC is the file format name Apple has chosen for the new HEIF (High Efficiency Image Format) Standard. Using advanced and modern compression methods, it allows photos to be created in smaller file sizes while retaining a higher image quality compared to JPEG/JPG.

Every iOS update comes with a host of changes, but some are not immediately obvious. ... HEIC will be used by default on new photos on iOS 11, and it's designed to save you storage space. As it's a new container format, there will be some incompatibilities along the way, and Apple does a good job at handling most of these.

To view these .HEIC images on Ubuntu, do this...

sudo apt update
sudo apt install heif-gdk-pixbuf
sudo apt install heif-thumbnailer
sudo apt install libheif1:amd64

Then save one of the .HEIC images to your ~/Pictures folder, right-click on the image icon, select Properties, and set the default application to Open With as Image Viewer.

Now a double-click on the image icon will open the file in Image Viewer for viewing.

Image thumbnails will also be seen in Files (Nautilus) windows.

In Thunderbird you can now also view these images in the original email attachment bar.