On: TextCaptcha: Simple Textual Captcha Challenges

[edflsafoiewq]

Is that a problem for this use case?

[shakna → edflsafoiewq]

They're matching checksums to prove it's a human. You can check these checksums, and find or create input that will match it nearly effortlessly.

So yes, I'd say that's a problem for this use case.

[edflsafoiewq → shakna]

I don't really see how. What does generating collisions get you? Doesn't this just require preimage resistance?