HEIC and Webp pictures
In Ubuntu 22.04: you have to install the package heif-gdk-pixbuf (no PPA needed):
In a terminal:
This will install libheif1 and libde265-0 along.
sudo apt install heif-gdk-pixbuf
sudo apt install heif-thumbnailer
sudo apt install libheif1:amd64
sudo apt-get install gimagereader gpicview
sudo apt install converseen
and then make Image Viewer (Afbeeldingkijker) or Eye of Gnome (Afbeeldingweergave) the default to open .HEIC images. And converse images using converseen.
As of May 2020, programs that support HEIF via libheif1 include:
GNOME Image Viewer (Eye of GNOME - eog) is updated in Ubuntu 19.10 and later.
GPicView version 0.2.5-3
GIMP 2.10.2+
Krita version 4.2
gImageReader (in Ubuntu 22.04)
heif-thumbnailer - a thumbnailer for HEIF images that can be used by Nautilus and Nemo.
libheif-examples – provides command-line utilities: heif-convert and heif-enc.
Online Tools
Google Photos and Dropbox both reportedly support HEIF.
There are other online converters (e.g. HEICtoJPEG), but check their privacy policies before use.
Miscellaneous
Imagemagick, as of 7.0.7-22, can be compiled with the --with-libheif flag.
tifig is described as "a fast HEIF image converter aimed at thumbnailing". However, it must currently be compiled from source.
Nokia HEIF Info and Source Code. However, Apple's implementation differs somewhat.
Webp pictures
For Ubuntu 22.04 you should install a ppa and the webp picture loader. To do that use:
sudo add-apt-repository ppa:helkaluin/webp-pixbuf-loader
sudo apt update
sudo apt install webp-pixbuf-loader
From now on Files wil show the contents of webp files.