Formatting title images
Main (title) images for articles, videos and topics
Articles, videos and topics have images that show up as thumbnails and overviews.
The best format for all these images is 2:1 (1440 x 720 pixels). A resolution of 72 dpi is enough.
Make sure that the image file is not bigger than 1 MB.
When you choose images, consider the following:
The main focus of the image should be in the middle - the thumbnails in the overviews (topics overview and articles overview in the topic) are not 2:1. They cut off parts of the left and right.
Here are two sources for free stock images: