[jansan]

The filter first creates pattern of 2x2 black squares, spaced by 8 pixels vertically and horizontally.

Then it creates a composite of the original image and the just generated pattern, basically coloring the 2x2 squares with colors from the original image.

Finally it blows up the 2x2 squares to 10x10 squares using the feMorphology filter primitive with "dilate" type.

A very clever filter indeed.