In some discussion on another thread, it was discussed how to get ONE RANDOM image (or text) to display in your app.
Front page: Just grabbing a random cell from the “Lists” tab in the A Column.
So only ONE of a list is picked randomly.
In my app, this image/text is only changed when the Spreadsheet is changed. So I have a form that only submits the current day and time (thus changing the random image)
You could also possibly configure this even more with a signed in user. The Welcome text could say something like: Hey Kevin, you are a winner!