Composition thumbnail images

You can choose which frame of a composition to show as a thumbnail image (poster frame) for the composition in the Project panel. By default, the thumbnail image is the first frame of the composition, with transparent portions shown as black.

To set the thumbnail image for a composition, move the current-time indicator to the desired frame of the composition in the Timeline panel, and choose Composition > Set Poster Time.
To add a transparency grid to the thumbnail view, choose Thumbnail Transparency Grid from the Project panel menu.
To hide the thumbnail images in the Project panel, choose Edit > Preferences > Display (Windows) or After Effects > Preferences > Display (Mac OS) and select Disable Thumbnails In Project Panel.