libheif-js (HEIC/HEIF image decoder) used by the image tools of this site.

Package: libheif-js 1.23.2 (LGPL-3.0), https://www.npmjs.com/package/libheif-js/v/1.23.2
  tarball (the exact files used): https://registry.npmjs.org/libheif-js/-/libheif-js-1.23.2.tgz
  build scripts: https://github.com/catdad-experiments/libheif-js (scripts/install.js pins the libheif release;
  the module follows libheif's major and minor version)
It is libheif (https://github.com/strukturag/libheif, Copyright (c) struktur AG
and contributors) compiled to JavaScript and WebAssembly with Emscripten; libheif's
decoder for HEVC-coded images is libde265 (https://github.com/strukturag/libde265, LGPL-3.0).

Licence: GNU Lesser General Public License, version 3 (LICENSE-LGPL-3.0.txt),
which is a set of additional permissions on top of the GNU General Public
License, version 3 (LICENSE-GPL-3.0.txt).

How it is used here: the package is used unmodified. The site's build tool
places it in its own JavaScript file, which the browser downloads only when
you open a HEIC or HEIF image, and it runs inside your browser. The source
of the exact version used is at the links above.