When uploading images to your campaign banner, you'll see that we list the recommended size as 1924 pixels wide by 824 pixels high (1924x824). An image in this size will look best when people view your fundraiser on a large desktop monitor.
Your fundraising page is responsive though, which means that it automatically adapts to the size of screen the person is viewing it on. If they have a screen smaller than 1924x824, they'll see the sides of the image being cropped as the site "responds" to the size of the screen. This is done in order to retain the overall look of the page (like your buttons, title, countdown timer, and more) on a wide variety of screen sizes.
How to format your images
As a general rule of thumb, you should format your images in a way such that all the "main" content of the image should fit within the middle 1170 pixels of the entire 1924 pixel wide image. Anything within this 1170 pixel wide "safe zone" will not get cropped, even on smaller screens.
Here's a diagram that shows you how this looks visually:
So if the main part of the content in your image is in the green "safe zone", everyone who visits your page will be able to see it no matter what device they're using.
The red box in the image above shows the full 1924 pixel wide image that we recommend you upload. Users with a large enough screen will see everything in the red box.
The green box in the image above shows the 1170 pixel wide "safe zone". Everything inside the green box will never be cut off, even if someone visits your page on a device with a small screen.