You can upload a variety of image sizes into your event page, however based on their size ratio, they will appear differently on the page. The file size of the images should be as small as possible, 1 MB or less for the fastest page loading. Below are some examples of what the page display will look like based on the image size. The examples use the Gallery Type of Single on the Event Settings tab.
Optimum image size is 800 pixels wide x 400 pixels high (landscape):
Image size 800 pixels wide x 600 pixels high (landscape):
Image size 800 pixels wide x 800 pixels high (square):
Image size 1200 pixels wide x 400 pixels high (panoramic):
Image size 400 pixels wide x 600 pixels high (portrait):
Image size 400 pixels wide x 800 pixels high (portrait):
Image size 200 pixels wide x 100 pixels high (landscape). Note that this image is blurry because the image size is too small: