I've noticed that JCE is using the preset versions when I upload my images. Basically, I uploaded a large file which is 1920 × 1080 px but JCE crops it at 800x600.
JCE does not resize images on upload unless explicitely configured to do so, and when it does, it does not put the resized images in a new folder as in your screenshot.
There may be another plugin resizing the images when the page loads in the front-end, or perhaps a feature of your template?
Ryan Demmer
Lead Developer / CEO / CTO
Just because you're not paranoid doesn't mean everybody isn't out to get you.