no tool exists to effectively detect plagiarism.

We are using some of the best available technology. However, you are correct -- no tool is perfect or fully effective. At some point, we may offer bounties for those who discover plagiarism that we missed, to increase the stakes and make the system even more robust.

Is it the case that if I wanted to make my content available here, I would first visibly insert my entire post, including text and images, into the comments section, then delete it and make it available for re-viewing?

That is correct. After you delete it and replace the content with "Ready for review" we will retrieve the deleted content and begin the review.

Still don't understand how that preserves the anonymity of the authors ...

There is no absolute anonymity implied (only a blind upvote process). In fact, the intent of the project is to get relatively unknown authors recognized. Mostly, their recognition will come via the weekly leaderboard updates. However, a curator who likes a given post can easily check to see who the author is (by looking at the beneficiary list), then follow that author.