What is a Facebook cover photo?
The Facebook cover photo is the big image that appears at the top of a timeline. You can use it to show something that gives people an idea of what you are like as a brand or person. The minimum size is 400 x 150 pixels, but anything less than 820 x 312 pixels can appear stretched. You will also get a better result if you use a PNG file for cover photos with a lot of text or a logo.