You install one of Bluchic theme, and setup as per demo site. However, there is no Featured Image showing up on your blog posts because you did not upload any Featured Image to your blog post all this while when blogging.
You want only one consistent branding image to show as all blog post Featured Image, but you really have no time to upload image to all blog posts.
You can install Default Featured Image plugin and setup a default featured image in your media settings.
Install WordPress Plugin
1- Go to Plugins – Add New
2- Search Force Regenerate Thumbnails in keywords
3- Click Install Now
4- Once installed, click Activate to activate the plugin
5- Go to Tools – Force Regenerate Thumbnail to regenerate all your thumbnail sizes.