Time domain filtering VS Frequency domain filtering in images

With this script I pretend to demostrate the differences and equivalences between filtering an image in the frequency domain and filtering an image in the time domain. It is a simple exercise very useful for those students of signal and image processing who are stating in this field. A good signal processing engineering must know how to filter in both domains.
The code is properly commented in English.
Any comment and suggestion is welcome.

Thanks,
Jesús Monge.