How to call the post thumbnail rather than the first image?

Hi guys: I asked for help about this in the plugins forum, but haven’t received a response. I feel like this issue isn’t specifically plugin related, so I’m posting it here too.

I’m using YARPP with a custom template. The template appears to be pulling and displaying the first image in a post, rather than the thumbnail. I have no idea why. I am hoping you’ll be able to look at the code of my template and help me understand how to call the thumbnail.

Thanks

[Code moderated as per the Forum Rules. Please use the pastebin]