A Sequence Generator Pro sequence can associate external JPG images with the current sequences.  These images, once associated, will be saved with the sequence file and, whenever the sequence is opened, the sequence images will be opened with it.  This feature is useful if you want to store a reference image (like somebody else's image) in order to ensure the images you are taking resemble the reference.  That said, a reference image can really be anything you want.

To use reference images, go to the "Sequence" menu and select "Manage Sequence Images".  You will be presented a dialog that looks like this:

To add a sequence image, click "Add" and then select the appropriate JPG image.  You will be required to give it a user friendly name.  To remove this image from the sequence, simply click "Remove".  Clicking open will allow you to re-open a sequence image if it was previously closed.

The feature integrates tightly with the Framing and Mosaic Wizard.  When you create a sequence using this tool, you will be able to save the working canvas as a reference point.  This will open up with your mosaic sequence so that you are able to remember what you were after when building it.