Selling your images online can be seriously complicated. You can try to submit images to some of the larger stock image marketplaces, but getting approved is tough. Even if you do get some of your images through, the marketplaces will take up to 85% of your royalties away from you.
You find priceless photography or filmmaking knowledge in online material. You start digesting it, but together with the precious free information, the author mentions a product or a service, which they obviously try to sell you. Do you feel you have been tricked?