Papers for Teaching an Introductory Course in Image & Signal Processing
I would let them read the paper about the Non Local Means Filter:


Antoni Buades, Bartomeu Coll, Jean Michel Morel - On image Denoising Methods.


The paper is readable and it is a great introductory to the Denoising operation in the context of Image Processing.
Also the Non Local Means is a very decent method (Result wise) even in our time.