How can I obtain famous articles which are not available online?
It seems that:


The first paper was published in Mathematical Morphology and Its Applications to Image Processing, J. Serra and P. Soille (Eds.), Kluwer 1994, ISBN 0-7923-3093-5 (a.k.a. Proc. 2nd International Symposium on Mathematical Morphology, ISMM 1994). Amazon link.
The second paper was published in Proc. DICTA 1999. Worldcat knows about the book. It seems that there are at least two Australian libraries that have it in their collections, so it should be possible to order copies of articles from them.


Fairly often, the interlibrary services of university libraries can provide copies of papers published in hard-to-find books and journals.

As Peter Shor suggested in comments, you can also try to contact the authors. Usually, authors will be happy to send you copies of their articles – after all, researchers write papers in order to make their results as widely known as possible.