This PSD file will demo a custom WordPress thumbnail for a post or page template using native WordPress functions. Not all post/pages have thumbnails so its common to use conditional folders with your thumbnails to display an image only when the post/page has a thumb. You can add any custom WordPress function to your design to render dynamic content in your theme output.
Testing the PSD
Use Exports View to render the WordPress theme, then upload to your server and test. You will need to activate each theme with a fresh install.
Using Exports View
Export the PSD in your required environment to see how shapes are rendered in your output.