https://neubias.github.io/training-resources/median_filter/index.html#2d

I feel doing the activity on the binary image may be a bit too technical.

I feel using one of the gray scale example images with a bit of noise might be more accessible for beginners as it may be easier to related the image to some biological sample.

But I am not sure.

@tibuch @manerotoni what do you think?