You can customize the Campaign Content of each campaign differently based on their type. Moreover, for each type you can set an image or a form to get the most out of your users. In all of the cases, it's best to preview your campaign before start displaying it to your users.
You can preview any campaign you build by clicking on the "Preview" button on the left sidebar:
You should be able to check the desktop and mobile preview of your campaign:
Most of the campaigns display an image to the end-user in order to increase engagement. Although you can define two images, one for desktop and one for mobile layouts, the aspect ratio does not always match the device of the user.
To make sure that users can see the entire image that you have uploaded, all images will be visible fully, without breaking the aspect ratio. This means that you might see empty spaces on the sides or on top or bottom of the image.
In some campaigns you can adjust the background color so that there is no big contrast between the image itself and the default background color.