When your theme is displayed in the Appearance section of the WordPress administrator interface, it is possible for a small screenshot to be displayed along with it. This allows users to see a quick preview of what your theme looks like with activating it or, in recent versions of WordPress, clicking the Preview button. The screenshot will also allow users to quickly differentiate it from the other themes listed in their Appearance section. If you’re planning on making the theme you’re creating public, then you should defiantly include a screenshot.

To include a screenshot in your theme, you first make take a screenshot of what your theme looks like. Methods on how to do this will vary depending on your operating system and image editing software available to you. Begin by taking a screenshot of your theme loaded in a browser. Next, load this into an image editor (anything capable of cropping and resizing will work) and crop out the browser frame in the screenshot. Then, resize your screenshot to 300×225 pixels (you may need to do some more cropping to get the ratio correct).

Once you have the screenshot resized, save it as screenshot.png in the root of your theme folder (where your style.css file is located). Then, you’ll be able to view your screenshot in the Appearance section. It’s that simple.