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iPhone HTML apps - Using an app startup image (app splash screen)

iPhone HTML apps startup image FAQ: How do I set the startup image (splash screen) for my iPad or iPhone HTML app?

This quick blurb from the Apple developer documentation leads us to the answer:

On iOS, similar to native applications, you can specify a startup image that is displayed while your web application launches. This is especially useful when your web application is offline.

By default, a screenshot of the web application the last time it was launched is used. To set another startup image, add a "link" element to the webpage.