The only way I know of to " stack" a cake like that is to use a caddy wampus stand or build your own from PVC. There are some great tutorials online on how to construct a stand like the one used on the cake in your photo inexpensively.
AYes agree with melanie. Cant imagine what else it could be. I would never trust myself to build one though. too paranoid.
AThe picture looks like they used 'Cake Stackers', it's a pretty expensive support system if your just making this one cake. In the picture, underneath the top tier looks like a metal plate-which is why I think it's a CS stand.
Here's a link with an alternative method, I haven't personally tried but it could be helpful.
Thank y'all!!! you all were very helpful!!