Thank you. I used Photoshop and a wacom tablet.
Some tips for the artists that are just starting off: I see that most of you are copying drawings by other artists. This is a good way to start learning how to draw. But what is even more useful to improve your skills is to try and copy photographs of subjects that interest you! I would recommend doing this as soon as you feel confident in copying drawings. It requires a bit more skill and insight then copying other drawings, but also makes it a lot easier to draw from memory later on!
I still draw from photographs on a regular basis, especially if I'm trying to improve my knowledge of a specific subject. At the moment, I'm improving on drawing mushrooms, pigs, rats and rabbits. I have a bunch of books about these subjects, and I try and draw the photos in them to look as realistic as possible. I studied dogs, wolves, ferrets and various insects before this. Which I can now draw by memory.
It's also useful to study the anatomy as much a possible. The best way to do this to do an autopsy (if the species of animal is easy and legal to obtain. Which rabbits, rats and (young and stillborn) pigs are in my area.). But I would not attempt this if you are younger then 18, have a weak stomach, or if you're just not well prepared. There are also some very nice anatomy books, some even especially made for artists, which can be used as an alternative.