See the docs for Fl_Multi_Label.
Some clarifications were made recently in the 1.4.x svn current
docs
including some example code for doing just an image/label pair.
Pull 1.4.x svn current for the latest docs, which have some
example code and some clarifications for how to use a single
Fl_Multi_Label. You'd have to make the doxygen docs.
Or, it just so happens I have a snapshot of the latest 1.4.x
docs
on my website because I'm working on the docs for a new widget,
and use my ipad to review it over the net:
http://seriss.com/people/erco/fltk/simple-terminal/structFl__Multi__Label.html
Note the example code under "
Example Use: Fl_Menu_Bar".
The use is similar for most label() oriented widgets, AFAIK.
Also in 1.4.x is some example code in
examples/howto-menu-with-images.cxx
A copy attached here.