The auto-captured thumbnail image is too dark, any way, I don't like the auto-captured thumbnail image.
Can I change it by myself?
Sure you can! you can set any scene on the video file to be thumbnail.

First of all add video file onto source list.

Please select the item you want to change, then click button. You will get a window popup as the following .

How to change the thumbnail image on DVD Menu and source list?

Drag slider No.1 to change the preview picture to be you like, and then click capture No.2 to capture the current image to be DVD Menu item and source list item thumbnail image.
: Capture image to be DVD Menu item thumbnail image and source list item thumbnail image.