Tried using Turbo?
Or, in Olde Opera, it works just fine.
Say, you set either no images or cached images as your default, then you can either switch it for any tab to load all the images, or you can click on an image's placeholder to show it.
Well, if one uses Turbo on Olde Opera, with images, the latter should load downsized.
Then you could either reload one in full quality or save it as such.
I've no idea if this nuOpera's Turbo would work that way or different though.