No doubt that the captcha work is way better than giving your retina for some WLD that the receivers would have to sell it asap on its market price if they need the money. Yeah right, there is no risk in that and their retina details are kept safe because they don't have to give it if they are only for the captcha jobs. But as for the WLD foundation, they're trying to make a huge database with all of these details piled up on it and will merge with a global record that they can use for anything that they want to do, as they say for some services but we can never know what's next to it.
And in my searches, I only found that only the hardware part of their scanner devices are open sourced. The software is closed source and we do not know how they're processing retina scans.
They're keeping it to themselves just like a large database that will cater the entire world's population of having the massive data of retinas for every country that they have been. That's why they've paid for some WLD to the people that have allowed them to scan their retina, it is the payment but at what cost when these people realize that it's too late for them that they've made a decision, regret will come eventually.