A well-chosen still image can tell a lot about a movie: its mood, how it was shot and what characters or actors are in it. This is true of feature films, and it is true of YouTube videos as well. A still image can can be used as a companion piece to a written review or preview, or it can be used to show friends what the video looks like. You can easily capture such an image using your computer system's native "Print Screen" function and an image-editing program.
Go to YouTube.com in your Internet browser and search for your desired video. Navigate to the video's page. The video will automatically play, but press the "Pause" button and let it load completely.
Click the "Fullscreen" button (to the lower left of the video) to make the video fill the entire screen. Click and drag the slider on the time line at the bottom of the screen to the image in the video that you want to capture. Wait a second for the slider and cursor to disappear from the screen. Press the "Print Screen" key on your keyboard (it may be denoted by a shortened form such as "Prt Scr").
Open your image-editing program and open a new project. Click the "Edit" drop-down menu and press the "Paste" key. Your screen capture will be pasted into the image editor. Click "File" > "Save" to save the image.