icoutils

http://www.student.lu.se/~nbi98oli/icoutils.html

The icoutils are a set of program for extracting and converting
images in Microsoft Windows icon and cursor files. These files
usually have the extension .ico or .cur, but they can also be
embedded in executables and libraries (.dll-files). Such embedded
files are referred to as resources. The icotool program converts
icon and cursor files into a set of PNG images. (Each icon/cursor
file may contain multiple images, usually of different sizes and
with different number of colors.) Icotool can also create icon/cursor files from PNG images. Previously icotool would generate XPM images, but as support for creating icon/cursor files was added, it was decided that generating PNG was better.