How do people do the 'Habbo Art' picutres?

So I have seen numerous people do this. People offer the service of making them for you, in exchange for creds.

Here's an example of what I am on about:

https://i.imgur.com/smAeQFu.png


Here's another forum user who has advertised that he can do it: https://www.habboxforum.com/showthread.php?t=844767

I just want to know what's the method they are using to do this?