The behavior of the default image tag has been changed. Images which exceed the maximum available space will automatically have their own scroll bar independent of the remainder of the post. As a result, large images should no longer force a horizontal scroll bar for the entire browser window.
Also, two new image tags have been created to allow you more freedom to display your images as you prefer.
[maximg] can be used to limit the maximum size of an image to fit available space. Larger images will be shrunk to fit the browser window, while smaller images will be unchanged.
[autoimg] can be used to automatically fill the available space in the post body. Larger images will be shrunk to fit, while smaller images will be enlarged. Extremely small images do not expand well, so keep that in mind when using this tag.
Both tags preserve the image aspect ratio.