Thumbnail

One image doing several jobs at once. It has to read at the size of a phone listing, make sense alongside the title instead of repeating it, and promise something specific enough that the right person clicks. Custom thumbnails need a verified channel; without one YouTube picks a frame from the video for you. The number attached to thumbnails is click-through rate, and the usual error is comparing that percentage against another channel or a published benchmark. CTR falls mechanically as a video's reach widens, so a video on 5 percent with 100,000 views can be a better outcome than one on 20 percent with 10,000.