I guess they forgot to ask. Someone prepared the presentation and needed a cool image just to see how the presentation looks like, so they used a cool and great picture. Why pay for it it's only a test to see how it looks and feels like. They gonna buy a photo ones things are done... so going on with the work on the presentation with this "current just for test" photo, well they got used to it, without even noticing that it's only a preview, test photo. They got so used to it that they started building the presentation around the photo, making it primary, give it more attention, all other elements should reflect the photos theme and style. By the end of the work on the presentation, people simple forgot that this image is just a "test photo" and nobody actually bought it/asked for a license, so when it was time to present the work, when asked if everything is fine, they simply said, "YES". Although, maybe, somebody knew that something was wrong here, but failed to admit it, so heck... Who'll know... and that's how your work probably got into a presentation without being asked.
The alternative is that someone stole your work, uploaded it to a stock resource website and people actually bought it without knowing that the real author of the work doesn't have a clue about it.
If you want to do something that works for both you and Billy, sue him for 20 million dollars. Shouldn't be hard to win this fight, in my mind. Afterwards, you take all that money except what you would have taken if they had asked for permission, and fund some CO2-saving research project... I bet Bill can afford losing this amount of money on his left cheek, and it may be a lot more than what he himself would have put into this (considering the fact that he's still one of the richest human beings alive and in history, I also bet he alone could fund the development of some sort of technology that powers half the US without a single pound of CO2-emissions within a year, and still have enough money to live a happy life, but until now it seems he rather sits in a comfortable chair and talks for a couple of minutes than actually do something about the problems he's talking about)...
I've maintained that I wouldn't be using Windows if it wasn't for the fact I rely on the OS for software and some of my hardware isn't Ubuntu friendly - this move by Bill Gate$ makes me wish I could move over to Ubuntu even more.
Retroactive compensation! Ask a lawyer for a nice letter, it's worth trying, especially during election time with all the noise about copyrights etc... It sucks to have to be guard dogs of our own creations but if we can't teach them how to behave, we still can hope for some sort of a compensation, right ?