Check out this iStock (Getty) photo on a "Free Wallpaper" site
It has the "iStock" watermark on it.
The site even includes a ready-made code that can be pasted into a website to display the image.
http://allbackgrounds.com/pot-leafs
The site claims that, "All images are property of their respective owners and are strictly for non-commercial use only."
But, everyone knows that in the event of a dispute the "owners" of the image don't care if the use was non-commercial or not.
S.G.