WordPress first introduced the “Post Thumbnail” feature in version 2.9. This feature allows the user to set an image as the featured image for the particular post. In version 3.0, the “Post Thumbnail” feature was renamed as “Featured Image”.
By default, this featured image option is not turned on. You will need to place a simple code snippet in your theme file to activate the function. Here’s how you can get it to work in your current theme.