Tumblr and Wordpress are blogging websites that allow their users to publish posts. Most users just publish their own personal posts on their own account. But these websites also allow a user to operate as an intermediary where other third-party users can publish posts through the first user's account.
Since Tumblr and Wordpress host the actual site, who has the duty to report child pornography to NCMEC if one of those third-party users submits it: The first user who created the blog, or the host of the site (Tumblr or Wordpress)?
Another way to consider the question is, who is the "internet service provider," the creating user who has administrative powers on his blog where third parties are submitting the offending content, or the corporate host of the entire social network?
Criminal Defense Attorney
A fascinating question, but there appears to be no actual event here that would trigger analysis. You can raise this theoretical question with an attorney or in a law school class. The large hosting entities have proven remarkably "teflon" when it comes to requirements to review and act on all content. The indirection implicit in these third party hosting arrangements probably insulates them further. I would be interested in what others here on AVVO might think.
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Anyone that comes into contact with child pornography should be reporting it.
With regard to your question of 'who is the ISP?" that is clearly the administrator of the blog and the corporate host. The user is just that, a user and is the one liable for the content. However, when we are talking about 'child porn', it is a game changer and everyone involved has a duty to report these crimes upon discovery.
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