That's what they want you to THINK! I'd be willing to bet that I could write a bot to break the captcha reasonably often.
Basically, you already have a 2/5 chance of getting the dup image one right, and a 1/3 of getting the math one right.
Telling the difference between the two is easy.
For the math ones, just use a decaptcher backend.
For the others, split the image into 5 images. Then, take the average R, G, and B of each image. Compare these. That will rate them on similar colors.
Count the white pixels in each image. Compare these. That will rate them on shape, since most of the pure white is outside of the image.
I bet 90% success rate.
Edit: I surfed > 100 sites without a bot.
account name is nimdaBTC
pay to 1CRHrw3DdtUuvBvYhZ5GK6fCFgZtRNn49y
Also, looking around the site, it seems that basically you are selling 0.01 BTC for $0.10
Bitcoins sent. BTW if you miss enough they will simply ban you. Heard many stories about people getting banned because they didn't pay close attention to the captchas and missed a few. But I guess if you want you can hack anything in the world.