All of your works would be considered to be a derivative work. This is because your work, is based on the work of someone else's. A good test for this to see if something is a derivative work is to see whether the new work can effectively exist without the original.
Most copyright laws worldwide are similar, thanks to the Berne Convention for copyrighted works. Since derivative works are normally a right that is exclusive to the copyright holder, you can't make such works without permission (generally through a license or expiry of copyright).
So now, let's take a look:
The Mona Lisa was made hundreds of years ago. It's definitely in the public domain. You're in no breach of copyright laws here.
Yes, of course. Microsoft retains copyright on their icons, and possibly trademarks as well. However, they may have trademark guidance that allows you to use their icons - as long as you follow it.
Likely the same as microsoft - you can assume it's similar for most large companies.
Code is copyrighted as a literary work - the layout and visual aspect is copyrighted as an artistic work.
That artist retains copyright, unless you obtain the work with a license, or the copyright is expired. If you create a derivative work, you infringe on their rights.
