To export a jpeg preview image also called "poster image" or "video still" you must use the "Video Still" marker in Squeeze. It is the lighter blue marker.
- First import your video into Squeeze.
- Next, click the Marker drop down on the left and choose "Video Still"
- Then move the play head to the frame you want (You can use left and right arrow keys to go on frame back or forward.)
- Then click the marker button or the "m" key on your keyboard to set the marker at the frame you are on.
- Finally apply one of your Stream format presets and click "Squeeze It!"