I upload a super Hi-Res image (2000×3000) to my Media Library and linked to it from the Jetpack Image Widget to display it in my sidebar. I was really surprised when WordPress really mangled the image when it was displayed in my Main Sidebar. How hard is it to display a thumbnail image even on the fly, although I would have thought the widget would have created or linked to a saved thumbnail anyway. Maybe it linked to a thumbnail that was meant to be displayed as a smaller image.
As you can see even windows did a better job at generating a thumbnail on the fly.