From now on, people with balance >= 0.00015 BTC cannot play free images. You can try your luck in Paid Images from now on.
This rule will not affect anything especially for real "faucet lickers"
They can simply withdraw their balance and then continue to play on the free images.
Of course before withdraw they need to make at least 1 deposit, but its not a big problem for them.
With the new rule, I think you should split the big 0.0003 btc prize in the free images into 2 or 3 smaller prizes, so to further reduce the incentive of withdrawing the prize.
Also I think you should add a captcha but only in the free images.