Last but not least, you can also earn money online by building an online community, although the monetization strategies you can pursue will vary a lot depending on your goals. You can build a community with a blog, for example. You can also build an online forum and charge people for membership. You could even build up a Facebook group and use your influence there to sell and promote products.
If you live near a university, there are likely all sorts of research studies looking for participants. While I was an undergrad at Virginia Tech, I got paid $500 to participate in a 6-week dietary study. The study provided all my meals and paid me, but I had to eat a 5,000 calorie diet of 50% fat for 6 weeks, plus I had multiple muscle biopsies, urine/blood testing, etc.
Turn your photographs into cash via sites like Fine Art America, which lets you upload your images to sell as prints, t-shirts, phone cases and more. Other marketplaces for photographers include SmugMug, 500px and PhotoShelter. Some sites require a subscription but may provide features ranging from cloud storage to password-protected galleries and a customized website.