I think it would be beneficial to be able to pass in a caption to an ePicture element when using the module in developer mode.  This would allow you to drop in a single hidden element accessible on every page.  Then you could add the popup effect to any picture and have a unique caption.  This may not be a big deal when trying to display images in a gallery mode, but when you have 30+ images scattered all over that you would like to add this feature to, not having to create an ePicture element for each image would be a huge timesaver and be easier to maintain.