A couple of quick thoughts: Its not really obvious to me what a "screenshot beautifier" _does_. It would be useful to have a (visual?) description of what it does without having to first drop a screenshot into it. I didn't have any screenshots to hand so fairly quickly clicked away. Pasting an image using Ctrl-V doesn't work for me (Win 10, Firefox 97.0.1)
I think you're right. There needs to be an option to try the app with some demo image. I've noted and will add it :)
Before you write any more lines of code add a picture to your landing page showing what it does.
No one who isn't a personal friend of yours is going to burn time trying an image editing product without first seeing an example of what comes out of it.