by text message or phone. You can do this by going to the verification page and entering your phone number to receive your verification code. You'll need to do this in order to ensure your YouTube account is accessible. Be sure to include the phrase "1280 x 720", "1920 x 1080", "3840 x 2160", or "7680 x 4320" as this is the best aspect ratio for a thumbnail.  Also known as 16:9 aspect ratio, this size is optimized for desktop and mobile viewing. While this can be a good option if you have no photos of your own, you can also use a frame from your video or even take a new photo to ensure you have a good quality image. Either right-click the image and select Copy Image or highlight the image and press Ctrl+C. Make sure you click the image before right-clicking it, otherwise, you will acquire a low-resolution copy. You can use Photoshop for more extensive image-editing features, though other image editors like GIMP also offer plenty of options.

Summary:
Verify your YouTube account Go to Google images and search for backgrounds. Copy the background you want. Open an image editor and insert the image as the background.