My question is - why does this require a server?
Write it in something that compiles to LLVM / WASM and just make a static page. Infinitely scalable and just pay for the domain (and CDN provider if applicable) both likely nominal cost.
You might still be able to offset a portion of the compute by just figuring out the URLs of the images on the back-end, sending that list to the client, which would then download and do the optimization / resizing.
I look forward to your version of this service, also to be provided for free, right? And for your sake, hopefully you won't have people in the comments demanding that you completely redo your project in the special way that suits them.
Is what I was responding to. Wasn't criticizing the posted product implementation choices or demanding a rewrite. I see how it could be read that way, which is unfortunate.
Parent comment asked a number of questions that all suggested a server was a requirement. If scale becomes any issue for a service like this, there are approaches other than shutting down the service due to server / maintenance costs.