Unfortunately, this is not a straightforward thing to answer. From the moment someone draws or creates something they own the copyright to that item. And how that art can be used it 100% up to the artist. It gets even more complicated if the owner then trademarks the art... as trademark laws are even more strict and aggressive.
How the art is allowed to be used is at the discretion of the creator.... Sometimes the original creator decides the drawing is free to use. Other times the artist puts it for sale on art sale sites or licenses it thru stock art sites. Or maybe they decide it is private art only and no one can use it. Any of these options are 100% the choice of the artist.... they created it so they get to decide how it is used.
However, sometimes other people who did not create the drawing take the art and use it for their own purposes or copy it or decide to sell it or put it on free stock sites... but they didn't get permission. Or maybe someone saw it and it really resonated with them, so they put it online because the liked it but forgot to include the ownership info... then it went around the internet in this fashion. It may look like it is free to use, however the artist was never given that choice and they still own the copyright.... Use of the art in any of these situations (and many others I have not mentioned here) is not legal.
As you can see, it is complicated. Just because it is seen in a google search, does not mean it is free to use.
Because of that, I highly recommend either looking for art on reputable stock art sites where license can be purchased if the design is used or using reverse image lookups to find the original artist of something you want to use and reaching out to that person. Many companies and artists are excited when someone approaches them asking to use their designs in the creation of something unique and happily give permission.
With permission, we know they are allowing the use of their designs and are respecting their rights and decisions.
Here is an article that I have on how to capture written permission for any art.