Could you please advise what does the field "params" do in link
options? (Misc tab) According to the code it isn't used anywhere.
I am trying to figure out if there is a way to attach an image to a
link in the menu without changing the core files.
thank you

Marcin

It accepts a key value parameters, handled by ParamsBehavior.

Eg:
foo=bar
spam=eggs

That will get you extra values when Link is fetched:

[Link] = array(
   'name' => 'some link',
   ...
   )
[Params] = array(
   ['foo'] => 'bar'
   ['spam'] => 'eggs',
   )
);

I can't recall how it will look exact, try debug($link) and see your
yourself.