The File Handling API enables web apps to register their ability to handle file types with the operating system.
This enables the file manager of the OS or other operating system flows to use the web app to open the file, just like with a native app.
Open the file manager of the OS of your device and select one or multiple files of type .png, .jpg, .jpeg or .webm by right-clicking it and then select this PWA to open it (make sure it's installed as a PWA first).
The opened image(s) will then be displayed below.