Mechanical Turk: Amazon's Mechanical Turk is a resource for doing human-intelligence tasks, or as the site commonly refers to them, HITs. You get paid a very small fee for any given HIT and you'll need a good deal of volume to make a substantial amount of money. But it is a resource you can use in your spare time to generate a small income online.
Join a startup accelerator: Another great option is to apply to a startup accelerator like Y Combinator, 500 startups, or TechStars, where a group of investors will help coach you, connect you with potential partners, and provide startup cash in return for a small stake in your company. The competition is tough to get into these, so don’t rely on them as your only path forward.
This isn’t to scare you off. I simply want you to know that this guide is going to focus solely on ways to make real, sustainable extra income online. Not just a few quick bucks. I want to share all the mistakes I've made that got me to where I am now so that you don’t have to go through them, and can build a successful online source of income for yourself.
If you upload photos of yourself, or friends/family with consent, it's worth going for the 'rights managed' licence option – otherwise you'll have little to no control over how your images are used (eg, you could star in an ad for haemorrhoid cream). See Alamy's page on understanding stock image licensing for more on the different types of licences.
Affiliate marketing is a big and profitable industry that covers a wide spectrum of topics and fields. If you have got an interest in fitness, you can make money promoting fitness videos or courses e.g. videos to loss your weight. In fashion wear, you can earn commissions by recommending friends to clothing or t-shirt of companies which are offering affiliate programs.