Reduced Size to Fit Post WidthWhen an image in their post or signature exceeds the posting area's width, their image is scaled down to fit within the posting area.
At Full Size with a Scroll Bar
When an image in their post or signature exceeds the posting area's width, the image is displayed at the same size with a horizontal scrollbar.
This setting does not affect image attachments, which are already replaced with thumbnails when placed in posts.
After you've made your selection, your settings will save.