As a public figure, you can take pictures of people in a public place, aka, expo, on stage, at a restaurant - and they can be put up. However, you can put their picture up with them endorsing a product or anything like that.
If there is a picture of Shawn Ray that he took in a public place, even with two girls, and is up on a wall, so be it. If that picture of Shawn Ray is also in an ad, or saying 'I endorse this product', then it gets into trouble.
I am always amazed at someone who comes to the expo, works in a booth, and then doesn't want their picture taken??? Hello... then don't work in a booth and promote the company you are working for.