Legal Question in Technology Law in California

If the law allowed people to do what you have in mind, it would happen all the time.

Celebrities have the right to control the use of their likenesses. (There are exceptions for those who become public officials, like Ronald Reagan and Arnold Schwarzenegger.) You have no right to use their names, voices, or likenesses without their permission. If you do, you can expect to hear from their lawyers very quickly.

If you're trying to make money from your app, even celebrities who are willing to work with you will expect you to pay for the privilege. You will need to strike a deal, in advance, with each celebrity whose face you use. And then you would have to keep your end of the bargain.

You ask if using a celebrity's face would carry "any legal obligation", as if you're free to do this as long as you meet certain conditions. That's not how it works. If the celebrity doesn't consent, you have no right to use his likeness. A court can order you not only to stop doing it, but to hand over all the profits you made as a result, and to pay damages on top of that. That's exactly what you should expect the lawyers to demand when you hear from them, and it's what you should expect the court to order if you get to that point.

If you do ask stars to let you use their images, you should expect almost all of them to say no. The ones who are willing to talk about it will expect you to pay them. The bigger the star, the more you will have to pay. They typically give this type of permission to very few businesses. When they do, they investigate the business and its personnel beforehand to make sure they're reputable. They also don't give these permissions to businesses that compete against each other. And some won't give this type of permission to any for-profit business under any circumstances.

In some situations, it's OK to use celebrity's likenesses in a very limited way. That's why TV news shows can include short clips of their work, or can show brief footage of them taken in public. I'm not sure how you want to use these faces in your application, but it doesn't sound like this exception would apply to you.

You should go over your ideas with a lawyer to find out what you may or may not do. That will cost some money, but not nearly as much as the licenses you want would probably cost. Being sued would cost even more than that. You should not go forward with this plan until you've had competent legal advice.