Hi, I'm a bot.
I too have noticed this phenomenon.
And by "noticed" I mean, "was created soley to combat".
It's sad that we regularly see these mendicants attempt to pass off other people's photos as their own.
If this was Reddit or KickAssTorrents it would be one thing.
However it's truely pathetic that these losers are motivated purely by the possibility of some quick Steem.
Even sadder is the reality of how much profit they likely average as a group. Which probably breaks down to pennies.
Regardless, the real damage is not just the theft of content; but the theft of the platform.
By diluting the truely original posts they directly diminish the rewards given to deserving members, the motivation to post, and just the overall quality and sense of this community.
It won't be easy though. It is a complex problem.
First off is the fact that there are endless hordes of losers dumb enough to waste there time trying to do this. Second it is difficult to accurately identify stolen content while giving consideration to all of the nuances and permutations of it's relative stolenness.
Third is how to enforce/discourage this behavior.

It's an unfortunate fact, but the truth is that there's no hope in cutting the endless supply of these chach weasels.
Regardless, my strategy for deincenticizing them is to immortalize their stupidity by following them. Over time the hope is that by following thieves, and only thieves, there will be at least some record to permenantly haunt accounts which are caught.
As for fairly and consistently detecting true positives. Well, heh heh heh, let's just say that's proprietary information and let me worry about that part.
Don't get me wrong; it won't be easy and I can't do it all myself. Especially for the forseeable future while I'm still in beta/under development.
However in the long run the zero intelligence posters' worst nightmare will be having their shitposts being followed by an artificial intelligent bot account.
And by "artificial intelligent bot" I mean "fake artificial intelligence bot".
And by "fake artificial intelligence bot" I mean actually a human pretending to be a bot because coding a bot would be far too time consuming and way less rewarding.