Go to Setup > Image Assets > Event Feed Banners
Click on Add New Banner. Enter the URL that relates to the banner image you are adding. Click on Select Image, navigate to the location of your image on your computer, then click Open. After you have loaded your image, click on Create Banner.
The dimensions for the Event Feed Banner are 640 x 122 pixels. The maximum allowed file size is 1MB, and supported file types are: PNG, JPG, and JPEG. Images are required to be in a RGB colour space to display correctly in our apps. CMYK images will be automatically converted, however this can result in a slight colour shift. To avoid this consider converting CMYK images to RGB before uploading.