If you are a professional photographer or have a real flair for photography, then selling your images on other sites could be an idea. This could be done alongside your own photography site, as it is a good way to help get your work viewed by a wider audience. There are numerous stock image websites to contribute to, but choosing a popular high-end site like Shutterstock should ensure your photographs make you some money.
Pro tip for first-timers: Carefully consider the pay rates that are listed. Penny Hoarder Carson Kohler has used the platform to find freelance writing gigs, and she reports low rates — like $3 for 500 written words. It’s probably not worth it. (And, yes, you’ll have to scroll through a whole lot of these low-paying listings to find the good ones.)
However, like anything else truly worthwhile, apps require a significant investment of your time or money upfront. If you don't have the skills, then you have to hire someone who can assist you in creating a great app. But first you need to come up with an idea that will sell. Do the proper market research and analytics to come up with the right app.