Commercial use requires 'releases' - editorial use doesn't. Stock photos can be sold for commercial (eg, marketing) or editorial (ie, journalistic) use. You'll have more opportunities to make cash if your photos are available for both, but photos containing people or property (including branding and logos) need signed releases to be sold commercially.
This has become a popular business model for online entrepreneurs over the past several years, and will probably just continue to grow in popularity. The best thing about selling online courses is that once you do the up-front work in creating the course and setting up your marketing strategy, you can get paid over and over again for work you do once.
Set up a roadside stand. Depending on where you live, you could profit handsomely by setting up a roadside stand. If you live near a resort area, for example, you could buy cases of bottled water, put them on ice, and sell them to passers by for twice what you paid. Selling fruit and produce you grow yourself is also a smart idea in highly-traveled areas.
How much will you make? I think my best month with Google AdSense was almost $5,000 over the last ten years. That amazing month blew my mind since it was actually near the beginning of my blogging journey. When you go from making zero to $5,000 in a month, that will rock your world. For me, it also got me even more excited because I knew there were other ways to monetize.