What size should my images be?

There are no fixed image size requirements for your campaigns. The ideal background image size for each campaign depends on how many elements you use in your campaigns and how much you drag the campaign to make it narrower or wider.

Here you can see how you can drag the campaign wider and add a Divider element to make it taller: 

Use the editing menu to change the size and position of your background image to make it fit perfectly in your campaigns.