No it isn't free at all and well enough explained why. As an educator you are aware of all this and that not acknowledging sources is simply stealing and plagiarism. So... 🤷♂
The change in this one picture is a start for sure. Though even this one is made/taken by someone. So if you want to source something properly, giving credit to the creator/owner is easy..: Use the creators name instead of 'image source' and link to their profile on the website they use.