Well first of all..how well do you draw? These are incredibly detailed and complex pieces that require a great deal of artistic skill regardless of the medium used.
It doesn't matter what medium the artist used. Creating an exact replica of these pieces of art will be VERY difficult even if you did know what medium they used. You can create similar images using almost any medium (digital, painting, colored pencil, etc.) as long as you are both comfortable and highly skilled with the medium you choose. I suspect that most of these were done digitally.
What I can suggest is attempt them with a medium you are familiar with and have fun with it.
Last edited by chanda95; 03-20-2015 at 11:54 AM.