I am not sure if this should be an end user option, especially since they might just be cutting and pasting. Instead I think this is a site-operator kind of thing.
How much should images be optimized prior to uploading: “noting|a bit|a lot” …
Name/value and default pending.
The results look quite excellent! Also, in combination… maybe we make this 100% automatic for certain cases? You set the “maximum” size of images on your forum to 2000KB and we have a heuristic that kicks in and makes sure we take care of stuff.