Don't measures based on computational difficulty have the effect of erecting an impossibly high barrier for those with limited access to such resources? (The poor, anyone using a mobile device, etc). Any system with a reasonably low bar can probably be worked around by a spammer at a low enough cost per account that it's unlikely to be of much use.
Some services (many subreddits, for example) use account age as a metric. That's easy to work around with mass registrations of zombie accounts though.
Some services (again many subreddits) use overall network reputation as a metric. That makes life difficult for new users though in addition to all the privacy issues surrounding centralized reputation and identity.
Some services use a phone number as a unique identifier that's more difficult to come by than an email or IP address. That still poses an accessibility issue and also introduces a privacy one.
Sorry, I don't actually have a solution here. Just a bunch of problems.
>* Don't measures based on computational difficulty have the effect of erecting an impossibly high barrier for those with limited access to such resources?*
I don't think this is true so much with the flattening of computational growth. These days a 10-15% general gain year over year is quite good, and we've seen gens with less. Order of magnitude is close enough in this case, there isn't that much practical difference between a week vs two weeks.
>(The poor, anyone using a mobile device, etc).
Case in point, for much of the population their mobile devices may well be their most powerful ones. A 7 year old PC can still be extremely capable, etc.
Also again, this is just another tool idea. A community can use it to whatever degree they deem appropriate, and that can vary dynamically. So in regular times a low volume community might set a very low level, just a few minutes worth say. But if there was a sudden influx, they could temporarily ramp it up for new joiners.
Some services (many subreddits, for example) use account age as a metric. That's easy to work around with mass registrations of zombie accounts though.
Some services (again many subreddits) use overall network reputation as a metric. That makes life difficult for new users though in addition to all the privacy issues surrounding centralized reputation and identity.
Some services use a phone number as a unique identifier that's more difficult to come by than an email or IP address. That still poses an accessibility issue and also introduces a privacy one.
Sorry, I don't actually have a solution here. Just a bunch of problems.