They are basically like the the ones you see in Digg.
I also thought about using arrows (like in StackExchange sites), but I think people are more used to thumbs these days (due to Youtube, Facebook and Digg).
I didn't make the thumbs-up button green because I couldn't find a green that looks good with the main red color. I also think that probably the thumbs icons are too small.
I would like to know if the user will notice the meaning of those buttons at first glance?
EDIT:
Is this better?
I don't think they are very clear actually. They seem to be on the smaller side too. You could go the You Tube way and have something 'like' or 'vote up' text next to the 'Thumbs up'.
I would make them 'green' at-least on hover with a 'tooltip'.@janoChen had mentioned that the site is for non-Taiwanese to interact (in another post), so the 'green' should be clear atleast to them.
Also, the cursor must change to 'pointer' when hovering over the buttons, doesn't look like it from the screenshot.
If you ask yourself the question, "is this clear enough", you already have an answer: it could be clearer.
Firstly, they don't look like buttons. It's only when you hover over them that you discover: oh, I am suppossed to click this image? A 3D-Effect would help.
Secondly, I didn't recognize the icon as a thumb at first, the YouTub-Thumbs (see @Kashyap) are much clearer.
Thirdly, if you want to stress that the only difference between the thumb up and the thumb down is that, well, one is up and one if down, you could put both on the same baseline, even if this needs more space:
(Oh, and if your question really is: "Is it clear enough?", then the answer is: ask your user. It depends.)
Your contrast is too low between background and foreground on your icons. Check out this side: http://www.snook.ca/technical/colour_contrast/colour.html
Even though it's mostly ment for text color contrasts, it's applicable for more situations, such like yours.
Don't forget that the thumbs up isn't universally a good thing:
"Thumbs up" traditionally translates as the foulest of gesticular insults in some Middle Eastern countries — the most straightforward interpretation is 'Up yours, pal!'[5] The sign has a similarly pejorative meaning in parts of West Africa, South America, Iran, and Sardinia, according to Roger E. Axtell's book Gestures: The Do's and Taboos of Body Language Around the World."[5]
In Bangladesh, Iran it is traditionally an obscene gesture, equivalent to the use of the middle finger in the Western world.
Though that doesn't seem to have stopped Facebook from using it.
Also: just draw the hand. Don't draw the sleeve.
