You can choose between two display modes for the image included in your In-App message. This can be done from the dashboard settings, in "Themes":
Cover : Batch will use the entire width of the screen to display the image. In portait mode, depending on the screen size of the user device, the bottom and the top of the image will be cropped.
We recommend a square file, with a width of 1200px. Make sure the important part is not in a zone that may be cropped (the red zone):
Contain : Batch won't crop the image vertically.
You will now have two empty spaces on the left and the right of your image.
If you choose the Cover mode, we recommend you use the same color for the background of your In-App message and the background of your image.
Introduced in Batch 1.14.0, In-App Image messages enable you to display a full-screen image or a modal with a close button or an auto-close timer.
If you want the In-App to appear like a modal, you need to upload a square image, with a width of 1200px.
If you want the In-App to appear like a fullscreen, you need to upload an image with a 2:1 ratio (for example 1200x600 pixels).
Since the In-App will adapt itself to the different screen sizes of the device, be sure to test the outcome on several different ones.
Introduced in Batch 1.17, In-App WebView messages enable you to display any web content in your app, while still leveraging Batch's campaign targeting, push and In-App trigger engine.
Any HTML content can be displayed, allowing you a wide range of possibilities.
Be aware that your message might be displayed in virtually any display size and aspect ratio:
iPhones (from an iPhone 5 to 12 Pro Max)
Tablets both portrait and landscape
Tablets in split-screen mode (1/3 of the screen) or free-floating windows
Use responsive web design techniques (CSS Media queries, Flexboxes, Grids, etc...) to handle this. Firefox, Chrome and Safari all come with tools that allow you to test your content on various form factors.