How does steemit cutoff bots?

Seems to me like the easiest way would be to use one of these(see below) to authenticate transactions

but obviously, none of us want to add an extra click to every transaction, nor should we.

So Perhaps we could have to do this with some n% of transactions

the next question becomes what percent, exactly is appropriate?

It ought be a high enough percent such that likely (this is statistics) it will weed out any vote bots before they have made X some number of transactions (also to be debated,) yet low enough that it does not substantially disturb normal usage of the site.

If X is say, a few hundred (100-300) then I imagine this could be as low as 5% or even less of transaction attempts tested, given that all we really can ever hope for is to defeat bots which are left to their own devices in a relatively timely manner. While true that somebody willing to baby sit their bot would be able to defeat this system, they would also still be wasting their time and largely defeating the original purpose of running a bot so that could discourage that behavior that way as well.

Just an idea, would be interested to hear from others about if it seems like a good idea and if so what % of transactions tested seems appropriate to you?