Most online image optimization tools upload your files to their servers.
TinyPNG does it. Compressor.io does it. CloudConvert does it.
Nobody says it out loud, but every time you optimize a client's images with one of these tools, those files pass through a third party's server.
WebAssembly changed that.
The same compression algorithms those tools run on the server, mozjpeg and libwebp, now run directly in the browser. No uploads. Nothing leaves your machine.
Privacy in developer tools is a problem most people ignore until someone points it out. We hand client assets to random services without thinking about it, because it has always worked that way and the files are "just images." But "just images" can be unreleased product shots, medical material, or anything under an NDA.
This is part of why I built Pikkx the way I did: compress, convert and resize entirely on the client, so the question of "where did my files go" never comes up. The answer is nowhere. They stayed with you.
Did you know your optimizer was uploading them? Or had you never stopped to think about it?