Postie – How to turn off thumbnails?

I’ve had good success with Postie thus far, but the thumbnails are always quite blurry in my CopyBlogger theme. Is there a safe/simple way to turn them off? I’ve been editing postie-function.php, but keep crashing my site.

I’d like to just post the image as I do when I manually upload the full-size.

Thanks in advance.