Flickr is making some interesting changes to their Terms of Service. After the changes take effect, if you want to provide moderate or restricted content, you will need to be a paying customer by upgrading to a Pro account.
Free accounts with Restricted or Moderate content will be considered in violation of our terms of service and subject to removal. Accounts found in violation of our terms will need to either subscribe to Flickr Pro or remove the content in violation.
The changes make sense, from a cost standpoint. Providing restricted or moderate content necessitates that Flickr provide more resources to content moderation. Therefore, to offset that resource expenditure, they are requiring customers to pay if they want to take advantage of those services.