I won't even bother to quote some of the comical suggestions about stopping piracy here.

The only thing that will work is having is an iTunes type site for porn with cheap ($0.99 per scene)/($3.99 per "movie") DRM free, H.264 encoded, a la carte porn. When you make the legit porn convenient, cheap, and all available in spot, a substantial portion of the pirates will start paying simply for the convenience/quality/reliability, just like they did with iTunes vs. the free pirated alternatives for music/video.

This will certainly not stop piracy -- some people have no money and have endless time while sitting at home unemployed, so they will keep pirating. But they never were or could be your customers. On the other hand the potential customers who do have money and don't want to waste time will come in droves.

Until the iTunes for porn (no subscriptions/cheap scenes/one central place where you can find everything) suggestion gets followed, porn companies will keep going out of business and piracy will keep getting worse. You have to offer people willing to pay a legal alternative.

There is a category of porn user who used to buy 100s of DVDs and now has stopped, because finding all the scenes that his porn babe of choice for the week has made is easy and free via tube sites. You used to get thousands of dollars from him, now you get zero. Until you offer iTunes for porn, he's not coming back.