It be like someone handing you a hard drive with 4 million pictures on it and asking you to pick out 4 pictures from all of them with the same person in them. It be almost impossible task that take your entire life time. Even using a computer to sift thought and look for key things would take days.
No, it's not.
You see they don't need to identify every picture.
What MS does is they create a hash tag for each picture, this is a mathematical equation based on the code of the item.
No, they do not care about your Aunt Lucy's wedding pics, or you ebooks, but what if they wanted to see who has a copy of the Anarchist Cookbook, the Bible, or a research paper on climate change. All MS needs to do is search the databse for the hash code of that specific book. It doesn't matter if you rename it, they can identify it. This is how they identify music and video piracy, as well as verify files are intact. So yes, it does work, I can send you a hash code and a quick search on Google will find it and give you a link to download it.
Now, you may not see anything wrong with having any of those three things, but what happens if you live in Iran and Iran wants to see who has a Christian Bible. This happened to gay men in Saudi Arabia when they were outed on social media. Or in the case of the US and our current president, decides to try and figure out who is LGBT and lead a war on them (which he is all but doing). Or how about being a Socialist or having porn, being a Socialist isn't illegal, but McCarthy made it pretty darn close to it and there are senators working to make porn illegal. Not to Godwin the discussion, but it was perfectly legal to be a Jew in Germany prior to WW2 when it suddenly wasn't anymore.
So while what you have may be legal today, or you THINK what you have is legal, it may not be tomorrow and computers don't forget. Stupidly downloading a copy of the Anarchist Cookbook today could put you on a list of potential terrorists for your entire life, possibly your kids as well. Not going to happen? What about a picture of Tracy Lords in her early "acting" career when she was doing porn while underage, you may not even be aware, and then somehow cops start looking into you thinking you are a drug dealer ask MS for all they have on you and OOPS, that picture pops up, now you are a convicted pedophile, even if you are not a drug dealer.
You don't control the data on your computer when running Win10, MS does and THEY decide who they share it with, and they are VERY happy to share it with law enforcement and government. Court order? You don't need a court order to buy information from a 3rd party you legally gave that information to.