How does "Appreciate" button in Behance works? vote once, not (only) cookies

How do you think Behance did their "Appreciate" button? (in the bottom of every page, for example: http://www.behance.net/Gallery/The-Jazz-09-Journal/349710)

You can only click once, after you click it says "thanks" and if you reload the page the button disappears.

If you delete the cookies, the button still doesn't show.

Anyone开发者_运维百科 has a clue? Do you think they check IP addresses?

Here is the way;) http://tutorialzine.com/2010/07/click-to-appreciate-badge-ajax-jquery-css/

From my experience of web design, that is the conventional way of making that happen (checking for IP addresses OR User-agents that is and not cookies). The way I know it is because:

1. Do it in Chrome, works for the first time and doesn't work subsequently
2. Do it in Chrome's Incognito Mode, doesn't work anymore
3. Open up Firefox, it still doesn't work

This means that they are using IP or User-agent to make this happen. It should've worked with Firefox if they were using cookies.