I think the holy grail of financial freedom is having so many passive income. This way you will never worry about your financial needs because everything is taken care of your assets. You will have all the your time in the world and visit all places you dream about. You have your time and money. This is the dream of most people which only few ever achieved.
When I purchase an existing online business, I look for cash flow over the past year and where the money comes from. I want the sources to be more passive so that it does not take a lot of my time. Also, typically I will make an offer that is 18 – 24 months of profit so that I know that I will get my money back within the next two years. I hope that helps!
The U.S. Internal Revenue Service categorizes income into three broad types, active income, passive income, and portfolio income.[1] It defines passive income as only coming from two sources: rental activity or "trade or business activities in which you do not materially participate."[2][3] Other financial and government institutions also recognize it as an income obtained as a result of capital growth or in relation to negative gearing. Passive income is usually taxable.

If an investor puts $500,000 into a candy store with the agreement that the owners would pay the investor a percentage of earnings, that would be considered passive income as long as the investor does not participate in the operation of the business in any meaningful way other than placing the investment. The IRS states, however, that if the investor did help manage the company with the owners, the investor's income could be seen as active since the investor provided "material participation." 
I’m a 45 year old business owner who also has focussed on diversifying my income streams. I have a short term vacation rental in Florida that I bought for $390k in 2012 and net rental income for the last three years has been growing steadily. 2015 I am at $70k gross right now but should end up at $80-85k with net around $45k plus we use the place about 35 nights a year.
Another benefit of investing in rental properties is the loan pay down. If you obtain a loan to buy the property, each month your tenants are paying off part of the loan. Once the mortgage on the property has been paid off, your cash flow will increase dramatically, allowing your mediocre investment to skyrocket into a full-fledged retirement program.
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!
Residual income is calculated as net income less a charge for the cost of capital. The charge is known as the equity charge and is calculated as the value of equity capital multiplied by the cost of equity or the required rate of return on equity. Given the opportunity cost of equity, a company can have positive net income but negative residual income.