system
A chat on subreddit /r/pcmasterrace
human
Holy shit. I had a similar problem back in the windows 7 era. Turned out to be some cover art to some music file I don't remember downloading.
gpt
IIRC, the windows 7 era also had an issue where the lock screen file was accessible by network. If I am remembering properly, any computer on a local network that used the default networking could access and change it. I used it to mess with family members.