Using ad networks like adsense doesn’t prevent you from targeting advertisers directly. In fact, that’s how I started; I searched the net for potential advertisers who advertised products relevant to my content and offered them yearly packages. If you choose this option, bear in mind that you’ll need to provide traffic reports and other site statistics.
Ebooks are one of my favorite sources of passive income. Now, you can do this the simple way and just publish it on Amazon's KDP. Or, you can go all out and build yourself a book funnel. Book funnels are powerful, but they won't be fully passive. For example, if you do a free-plus-shipping offer for your ebook (converting it into a physical book), you'll need to create some one-time offers (i.e. extra training) and up-sells (i.e. an audiobook). But, a book funnel can be very powerful.
Invest in dividend securities. Some stocks provide shareholders with regular payouts called dividends. For very large, old companies, these dividend payouts are made for consistent amounts and can amount to a substantial income if you own a large number of shares. Look for companies that are very established and have been paying dividends for a long period of time (more than 10 years). You should be able to find this information with a quick online search.
Passive income is earnings derived from a rental property, limited partnership or other enterprise in which a person is not actively involved. As with active income, passive income is usually taxable. However, it is often treated differently by the Internal Revenue Service (IRS). Portfolio income is considered passive income by some analysts, so dividends and interest would therefore be considered passive.
If you have specialized knowledge in a certain topic, you can put together an online course to teach others. For example, if you have experience in real estate investing, you can create an online course “Real Estate Investing 101”. The benefit of an online course is that once you create the course material, you can sell it to as many people as you want.