The Hub of the Day is selected by HubPages staff. In order to be selected, you must, of course, write a quality article that is worthy of being selected as Hub of the Day.
In addition, you must make sure to show that all of your graphics are legally allowed to be used, either by using your own images, or making sure that they are properly attributed. See this hub to learn how to find free legal images and how to attribute them.
The hub must also come to the attention of HubPages staff. A quick and easy way to do this is to write hubs that relate to the Weekly Topic Inspiration. You can find these in the Forums. You don't have to use the current topic (you can use older ones), but the newer ones tend to be higher on the staff's radar. These titles have also been researched, so even if you don't get Hub of the Day, you may get good traffic on them anyway.