A lot of this latest was filmed in Hawaii and some of the locals were casted for many of the background scenes, but if you wanted to be casted as one of the pirates, you had to be skinny as well as ugly.
I got this info from a skinny and ugly friend of mine who appeared in a few shots with Capt Sparrow and his gang of sea-going scallwags.
And I have to admit that he was one hell of an ugly pirate.
He even bragged that the make up crew only had to dirty his face a bit.