It's a very basic DRM. I think someone who really wants to crack it can do so, but for a small indie game in development, a true hacker might not bother. It would be somewhat troublesome and a waste of time. Achieving this level of protection is sufficient.
The game's code is obfuscated and then further protected by a shell. This shell prevents the game from starting if a debugger is running (Cheat Engine comes with a debugger).
The game does not require users to stay online. It only needs to connect to the server once when entering the captcha. If the captcha is entered correctly, the player can receive very valuable in-game items as a reward . (you can think of it as an NPC giving the player a puzzle every day, and if the player gets it right, they receive a shiny unique gift).