Freelancing via the Internet is a great way for experts in their individual trades to help a variety of clients overall. Several freelancing and project-based websites let businesses that need extra help to list their projects. Small businesses and freelancers offer proposals, ideas, or bids, whereby the buyers can easily choose what they want and need. Sites like Elance or Upwork cover just about everything including writing content, creating graphic design, programming, and data entry.
Photos of people can only be sold for commercial use if they've signed a 'model release' that gives you permission to use their image (children need a parent/guardian to sign). Without a release, these photos can still be sold for editorial use, as long as they were taken in a public place – eg, if you submitted a 'breaking news' shot with people in the background. If there's any doubt, always ask permission.
Regardless if you need to earn some fast cash or we're just talking about making money in the grand scheme of things, there's an important psychology that needs to be mentioned before getting into the strategies. If you study Freud's model of the mind, you'll discover the Psychic Apparatus. It's the three-part construct in your mind that controls all of your behavior.