Template customization -> jrGallery -> can't find (datastore key)'s to make correct call
Design and Skin Customization
The problem here is you are not telling the system WHAT image you want to show. When displaying a profile (or user) image it is easy, since all accounts only have ONE of them. But you could have a THOUSAND gallery images, so the part missing here is you need to get the _item_id of the LATEST image uploaded, which is going to require a jrCore_list call to get that info, as well as as small custom template to just return the ID.
Is this going to be loaded on every page? If so I would recommend a custom module or smarty function instead of doing it with a jrCore_list call.