Custom forum rank pictures

Hello, and sorry if this has been asked before. I tried searching both in this forum and the FAQ.

So, I would like to set my own custom forum ranks, complete with their own pictures. I am using a WW2 military theme, so I'd like the ranks PVT-COL with their insignia's. Is there any way for me to set custom ones, like here: http://prntscr.com/7b0cs7. I can't figure out how to edit them. 

Also, is it possible to have more than six?

Thank you ahead of time.

AP > Users & Groups > Ranks
Create the ranks and add the image URL in the box for image.