Okay, this is now done! Mousing over the thumbnails in the gallery will now display the date and location of the photo in a tooltip.
This means that if you have previously been putting that information in the caption, each image needs to be edited to put those into the proper fields. I took the liberty of editing the images in the entry linked below so you can see how it works.
Hen and Chicks (Sempervivum arachnoideum subsp. tomentosum)
