I think it's not really clear if the AI flood is just like Photoshop, and what the long-term effects are.
I hate to say it, but Taylor Swift specifically hasn't seen anything yet.
An image is quite unique in it's hash/signature, but a video generate by AI can have billions of unique seeds.
Maybe don't allow companies you don't trust to buy ads?
If only companies with a relationship with your sales team can buy ads from you, and they know they'll lose that ability if they run a fake AI ad, then you have far less to worry about.
It could be argued that this may work for newspapers, TV, and radio stations, but can't scale for serious websites. Serious websites won't be taken seriously if they can't get this under control, and folks will be turning back to newspapers, TV, and radio stations to get away from it. Don't make them competitive again.
The only way this will effectively be dealt with is:
1. Banning the people caught doing it from social media.
2. The law enforcement/judicial way.
I don't know if new laws are required, there's probably something that already applies. E.g. if you Photoshop people in various ways and distribute the images, I'm quite sure the perpetrators get punished.
While it would probably work, it sounds prohibitively expensive.
Within limits. If, say, said artist posts from their own account, signs the art, or otherwise links the deepfakes to themselves, then this could be unauthorized use of someone's image in order to benefit by raising their own status or otherwise profiting in another way than direct sales. I'm sure that's actionable.