1) Find a definition and briefly explain what matte painting for film is.
2) Plot out a brief history of matte painting describing the key points in its development and use in film and TV.
3) Find a use of it in a film and analyse why it was used, how it was used and critique the final piece (is it convincing etc).
Again - just like the research for the green screen - starting with wikipedia (here and here) is useful as long as you use the references at the bottom of the document.
Also have a look at the following articles and videos:
How digital matte painters work
The best matte paintings of all time