Wow! What an awesome list! My favorite is the stock photography because I love photography. I have had some success there, particularly with one photo I make some decent income from. I think the key with stock photography is finding a shot that is high demand. Then, find a new unique way to frame that shot. This is the reason my St. Louis Arch photo is a top 10 on both ShutterStock and iStockPhoto. Thanks for the awesome ideas above!
Ebooks, which can be published through sites like Amazon Kindle Direct Publishing, are an increasingly popular option. Because these books are self-published, the process is quicker, allowing you to build residual income faster than the traditional publishing route. Whether it’s a romance novel or a how-to book on fly fishing, you can create a book and have it available for purchase in a matter of weeks.

Do you know of a successful business that needs capital for expansion? If so, you can become something of a small-time angel investor and provide that needed capital. But rather than offering a loan to a business owner, you instead take an equity position in the business. In this way, the business owner will handle the day-to-day operations, while you will act as a silent partner who also participates in the profits of the business.
YouTube brought in nearly $4 billion in estimated ad revenue in 2018. So you can earn a potentially large income by uploading videos to the platform and then watching those ad dollars roll in. You may need or want to upload videos regularly, which isn’t especially passive. But you don’t need to provide a specific product or service directly to customers.
If you're looking to get started in real estate, look at a crowd funding solution like RealtyMogul. It works similar to LendingClub - you commit as little as $5,000 towards a property. When the property is fully funded, you become an owner, and will receive your share of the earnings and appreciation in the property.  Check out RealtyMogul to learn more.