I will start with the following question "why signals can be
compressed?". I will then describe quantization, entropy-coding,
difference-PCM, and Discrete Cosine Transform (DCT). My main 
motive will be to illustrate basic principles rather than to 
describe details about methods. Finally I will discuss how 
these various algorithm combined to get the JPEG standard for
image compression. Time permitting, I will comment on various
famous theories which lead to JPEG standard.