Bear in Mind the Size Restrictions
Facebook’s cover photos come in a weird size. They’re 851 x 315 pixels (roughly a 2.7:1 aspect ratio) in a desktop browser.
And they’re 640 x 340 (about 1.88:1) pixels tall on mobile.
Any photo you upload is displayed automatically at the size and shape. If you upload anything smaller than that, Facebook will enlarge it, making it look blurry and ugly.
Facebook cover photos are also 100KB in size. Facebook automatically reduces images to this size, if you’re interested in having the highest quality image possible, do it yourself.
Think How Your Image Will Look on Desktop and Mobile
Since your cover will look different on desktop and mobile (and also appear a full sized image in any aspect ratio when people click it), you need to think about the photo will look in different places.
You can reposition your cover photo on the desktop, but on mobile, your cover photo is automatically cropped at the top and bottom to fit.
You also need to think about how your Profile Picture and the other interface elements affect your cover photo. On the desktop, your profile picture and name will obscure the bottom left corner. The Message, Friends, and other buttons will obscure the bottom right corner. There is also a subtle dark gradient, so things towards the bottom that aren’t blocked will look slightly darker.
On mobile, all the buttons are below the cover photo. Your profile picture, however, blocks off a chunk of the bottom center.
All this means that you should ideally choose a photo where the subject matter is focused in the center of the image. If it’s at the bottom, it’s just going to end up cropped off or blocked by interface elements.
Pick Something Meaningful
Your cover photo is public. It’s one of the few things that anyone who views your Facebook page can see. This means you should probably pick something that represents you. Other people go with quotes that mean a lot to them, photos of their family, images of their hobbies, and more.
Try a 360º Cover Photo
There was a big trend a few years ago where people tied their profile pictures and cover photos together as one big image. Since, your profile picture appears in different positions depending on what device you use, it doesn’t really work anymore.
Nothing’s stopping you from being creative. Facebook now supports 360 degree cover photos, which are certainly eye catching and different. Just take a 360º and upload it as your cover photo. You could also use a panoramic image that isn’t a full 360º.
The big difference with 360º photos is that while they only display as 851 x 315 pixels (or 640 x 340 pixels on mobile) image, people who visit your page are able to drag the image to see the rest of it.