Watermark, watermark, watermark!
I know there are those who will take the time to remove the watermark. I know that it is less work to modify the picture than to do the work. But as time goes on, the lazy will be lazy and move on to lower hanging fruit.
Also, I would love to see the Dev team of Steemit announce some countermeasure. Users of @steemit would be so grateful, and investors in the assets backing the platform would become even more of evangelists for the platform.