The cover image on company profile serves as a visual anchor of the profile page. A company typically uses this image to make a statement about their brand or business, or updates the image based on specific promotional events such as a new product launch.
The minimum dimension of the image is 2000px (width) x 270px (height) so that on big desktop screens, the image appears optimal under full width. On devices (or browsers) with smaller width, only part of the image can be displayed. See the visual guide below on how the image would appear on desktop/tablet/mobile devices.
When you choose or create the cover image, it is important to keep in mind of the “Mobile Safe Area” (350 x 200). If there is a particular focal point in the image, such as an embedded headline text, it is better to fit it into this area, so that the image will appear properly on all devices.
The same guideline applies to the cover image on user profile as well.