Stock photos boost posts. They also cost money. If, that is, you pay for them. I wonder how many people are pulling content off Google without paying the rights holder. This could be a big legal issue if Getty Images or iStockphoto etc. decide that this is a site hosting pirated content.
And Steemit's posting process encourages this - the only way to insert a pic into a post is... through a web link. Unless (as I did here) you pay for the pic and upload it to your website's media folder, the site is practically encouraging the use of unlicensed content.
You see this kind of thing on Goodreads, or Facebook, but the difference here is that people are being paid for the content they're posting. And, I can see the big photo sites deciding that someone who's being paid $$$ for a post, using their unlicensed content, needs to give it up. (The "Bittersweet Symphony" effect.)
Actually paying for pix might be worth it, if you have an unlimited account at a photo site or have taken advantage of big sales that reduce pic costs to $1 apiece. Or, it could be a loss if you make $0.00 on your post. (This pic cost me $1, so technically this post is at - $1.00 at posting time...)