Congratulations on building this! I certainly do agree with the fact that there are a lot of sites that force you to upload, ask for your email, and sometimes even add a watermark to the image; amongst other unknown things.
Although from first look, I can tell you that there's a lot of text on the site and it's a bit too cramped. From my perspective, tools like these should get out of the way and the UX should be self-explanatory for an image "conversion" tool. Basically, just a box to select, drag/drop images, a few user inputs such as the output quality and format. That's about it. A single line at the top explaining what the tool does (and that it is local) should be good enough.
Also, the title says "PNG to JPG converter," but the rest of the site claims it can convert to quite a lot more than just those format. You can possibly change that to, as an example, something like: "ImageConverter - Convert images between formats, locally". And you can get rid of multiple pages, turning it into a single-page with all the possible output options.
As a sidenote, I've been using Mazanoke for this: https://github.com/civilblur/mazanoke. It's not my project, just something I happened to stumble upon a while ago, but it's similar to your project and works exactly like you would want it to.
From my test, the rest of it works great. Good luck!