Distinguishing Spoken Speech from Played-back Recording of Speech Do any general-purpose techniques exist to distinguish live spoken speech from played-back speech samples? For example, if I were to deploy a speaker verification system to authenticate users by voice, I would not want the system to be able to be spoofed by playback of voice recordings. 

I think I can imagine at least one technique which might work for certain known combinations of microphones / speakers: If a microphone of sufficient quality captures a novel signal outside the speech band that corresponds (in time) to a signal within the speech band, this would seem to indicate a high likelihood of the sample not being a live speaker (because live speakers don't emit signals outside the speech band). Is this reasoning sound? (No pun intended).
Do any general-purpose techniques exist to distinguish live spoken
  speech from played-back speech samples?


No, at least not how I understand your definition. 

Consider the case of  "live speech" : some one talks into the microphone, you digitize the signal and analyze it. You can also store the digitized speech and analyze it a day later. Now the exact same samples constitute "play back". Since the samples are identical, you can't distinguish them from "live speech".