How do I display an image using the Dynamic Background module?
Make sure you also completed the required configuration steps as described in the Readme.txt of this module. I.e.:

Enable the modules/extensions that you want to use and go to the administration interface at /admin/config/user-interface/backgrounds/settings. Start by filling out the form and remember to fill out the CSS behaviour section. Then go into the configuration tab for each module/extension that you have enabled and as a minimum filling out the CSS behaviour fields.
Go to /admin/config/user-interface/backgrounds and select some images to upload after pressing &quot;Save configuration&quot; the form will change and allow you to select a default image. If you have enabled some of the extensions go to their location and select one of the uploaded images. See the extension descriptions above for information on where to select images for each extension.