The originator put the content up FIRST. Does that make it a little easier?
Not trying to pick a fight, but that's not as easy as it sounds ... Last modified dates can be spoofed to a bot easily, and (especially if people run an article publishing site that gets scraped a bunch) if GoogleBot spiders the other page before yours they're the originator not you ... I think 'spidered first' is the answer, because then it makes a DMCA to replace the offending copiers easier since you only need to send Google and the site (or hosting provider of the site) they have listed a DMCA complaint to get your original copy the credit it deserves, but it's definitely not as easy as it sounds, because their bot isn't you, so knowing who put it up first has to depend on where the bot found it first.
You put up a new page. Page gets scraped. Scraped page gets spidered 1st. They're the originator, not you.
[edited by: TheMadScientist at 8:04 pm (utc) on Feb 28, 2011]