File Roulette is an app developed by ex-Geckoboarder Daniel Upton that generates a URL that returns a different file in your Dropbox each time you visit it – either randomly or in sequence. This tool can be used to create an image widget that displays a new image after every refresh, which occurs automatically every hour.
Add a new Image widget from your dashboard and give it a Title.
Open file-roulette.com in a new browser tab or window. Then, click Log in With Dropbox.
Dropbox will ask you to allow File Roulette access to a folder. This will create a "File Roulette" folder in the "Apps" folder in your Dropbox.
You should be presented with 2 URLs: one for random order, the other for one after another (Round Robin) order. Copy one of these to your clipboard.
Return to Geckoboard and add a new Image widget.
In the URL field, paste the link you copied, then click Save.