This picture has been made by writing original C++ code on a computer. It is a fractal and its mathematical name is a "Sierpiński Curve Julia Set". It was created using the dynamics of a complex rational function.
Much larger canvas or paper prints can be created if required, with no loss of quality. (Currently the largest size for a print is around 200 x 150 cm.)
For more information:
https://gcboore.com/pages/cd6b-julia.html
https://gcboore.com/