Problem with thumbs

I am having a problem with this plugin. Thumbs are not displayed for some posts, instead some other images (like an apple image or an ice crystal etc) are being displayed which are totally irrelevant.

I have 2 images for my posts (which is a custom post type). One is video thumbnail and the other is featured image. Apparently, instead of using featured image this plugin is trying to get video thumbnail.

How can I edit it to use featured image instead?

Thanks