Even in the few answers here, people widely determine the internet to be a 'anything goes' public domain. Most people, if anything, think exactly what these here are answering, that if it's on the internet it's for the public.
That's absurdly incorrect. The internet is not the public dumping zone where anything you see is yours for the taking.
This default thought is driven by obscene selfishness and lack of consideration.
You don't google 'Mona Lisa' and just right click, save file and boom that's now yours. Why? Because you recognize the Mona Lisa as someone else's production, someone else's work, someone else's property. Do you make it your wallpaper or phone background? Yeah, sure.
It all lies within what you choose to do with what you find. Some things you can do are considered commercial. Some are not. There are different forms of 'rights' to things. If I create a font and it's available for download on a public site, is it free? You don't know until you've read into it far enough, just being able to download it and use it immediately doesn't make it free. It may be royalty free, but not commercial free. It may be free for personal use, but require licensing for commercial use.
Generally, through sheer will of giving credit where credit is due, people should always seek the true source of any image they find on the internet and look to fulfill the requests of the provider of said image.
Many shy away from costs that come with downloading images, but more often than not, people just want credit and recognition, artists usually, but people in general don't want to be overlooked and may be seeking compensation.
Even if it's entirely in the form of acknowledgement.