YouTube video thumbnails directly influence the number of views your videos receive because these little images appear in viewers' search results list. If your thumbnails are interesting, they may attract additional viewers. You are prompted to select a thumbnail when you upload a video, but can also change the thumbnails of existing videos. You can upload custom thumbnails for your videos as long as they meet YouTube's size and format requirements and respect the community guidelines.
Change Video Thumbnails
Log in to your YouTube account, click your picture in the upper-right corner and select "Creator Studio." Click "Video Manager" in the left pane and then click the "Edit" button next to the video you wish to edit. Select one of the thumbnails generated by YouTube from the list to the right of the video, and then click "Save Changes" to save and apply the changes.
Upload Custom Thumbnails
To upload custom thumbnails to your videos, you must have a verified YouTube account. To become verified, provide your phone number so you can receive a code as a text message from YouTube, then enter the code when prompted. Click the "Edit" button next to the video in the Video Manager, select the "Custom thumbnail" button and then upload the thumbnail from your computer. Click "Save Changes."
Your thumbnail images should have a resolution of 1280x720 pixels; a minimum width of 640 pixels is mandatory. YouTube accepts images in JPEG, GIF, BMP or PNG format. The size of the images must be less than 2MB. Images that are sexual, violent or graphic in nature may cause YouTube to age-restrict your video.