Adobe's web-based JPG to PNG converter is exactly like this. Upload a JPG, hit convert - it uploads the file, processes it on their end, and then refuses to give you the result until you "sign up for a free adobe account that we conveniently didn't tell you about until now!"<p>Similar enough - some shopping websites will grab your email address when you start doing a guest checkout but eventually decide not to purchase from them.
They'll then start spamming you without your consent a day later.<p>Ransom sign-ups belong in the same tier of horrible.<p>Modern downloadable software does this too. You download a "free" partition manager or "free" PDF converter, or whatever "free" - you install it, get through their wizard/main workflow to do what you want, but then it says "oops, sorry, you have to pay for this!"<p>Anti-consumer stuff it all is. What a shame software and websites like this are allowed to exist.