DavidFromOttawa

I had the same problem. I used Fourteen Extended plugin to make the page content wider. I set Content Max-width to 874. When the browser window is wide, the left and right floating images protrude outside the container. This seems to be a design feature, but it only works with the narrower content width.

The problem is in Twenty Fourteen’s style.css, where, for the widest browser width, it sets margin-left or margin-right to -168px. You could just comment out this line in style, or preferably, create a child theme as follows:

/*
 Theme Name:   Twenty Fourteen Child
 Theme URI:    http://www.petrieisland.org/wp/twenty-fourteen-child/
 Description:  Twenty Fourteen Float Image Fix
 Author:       David Villeneuve
 Author URI:   http://www.petrieisland.org
 Template:     twentyfourteen
 Version:      1.0.0
 Tags:         light, dark, two-columns, right-sidebar, responsive-layout, accessibility-ready
 Text Domain:  twenty-fourteen-child
*/

@import url("../twentyfourteen/style.css");

/* =Theme customization starts here
--------------------------------------------------------------

When I used the Fourteen Extended plugin to widen the content area of pages,
(by default 474px, I increased to maximum of 874px)
it caused images to float outside of the page boundary.  This also occurred
if I used columns or boxes.
The fix below will keep the left or right aligned images inside the container.
The only change is margin-left and margin-right were -168px, now 0px.
David Villeneuve 8 June 2014.
 */

@media screen and (min-width: 810px) {

	.full-width .site-content blockquote.alignleft,
	.full-width .site-content img.size-full.alignleft,
	.full-width .site-content img.size-large.alignleft,
	.full-width .site-content img.size-medium.alignleft,
	.full-width .site-content .wp-caption.alignleft {
		margin-left: 0px;
	}

	.full-width .site-content .alignleft {
		clear: left;
	}

	.full-width .site-content blockquote.alignright,
	.full-width .site-content img.size-full.alignright,
	.full-width .site-content img.size-large.alignright,
	.full-width .site-content img.size-medium.alignright,
	.full-width .site-content .wp-caption.alignright {
		margin-right: 0px;
	}

	.full-width .site-content .alignright {
		clear: right;
	}
}