Each section with the option to upload an image (a "Browse" button) is designed so that images must meet a minimum image size to display correctly (or at all, in many cases). 

If you click "Browse" and upload an image from your computer, you will see the minimum size displayed below the upload button. If you choose an image that doesn't meet the minimum, you will receive an error message.

If you navigate to the media library to browse for an existing image instead of uploading a new one, it is possible to choose one that does not meet the minimum size and you will not get the error message. If an image that does not meet the size requirement is selected in this way, it will appear on the back end (in editing view) but will not display on the front end (what site visitors see).

Minimum Sizes for Images

Article

Header Image: 1366 x 548 pixels

Thumbnail: 600 x 600 pixels

Basic Page

Intro Background Image:  1366 x 480 pixels

Book

Book Cover: 200 x 450 pixels

Event

Header Image: 1040 x 526 pixels

Thumbnail: 600 x 600 pixels

Image Card

Thumbnail: 600 x 600 pixels

Multipurpose

Introduction

Background Image: 1366 x 480 pixels

Main Content and Sidebar

Icon: 420 x 300 pixels

Video Spotlights with Articles

Image: 800 x 800 pixels

Dark Callout

Left Image: 800 x 800 pixels

Spotlight - Video

Image: 800 x 800 pixels

Spotlight - Static Image

Image: 800 x 800 pixels

Spotlight - Fullscreen Video

Image: 1366 x 800 pixels

Fullscreen Slideshow

Image: 1366 x 800 pixels

Timeline

Header Image: 1366 x 480 pixels

Static Slideshow Image: 600 x 600 pixels

Slide Background Image: 600 x 600 pixels

Gallery

Image: 600 x 600 pixels

Person

Headshot: 684 x 684 pixels

Testimonial

Testimonial Image: 680 x 680 pixels