Hi Jon,
Are you planning to import the photos from an external folder or are you dragging the photos in TW?
FMLK...(from my limited knowledge). If you are dragging the photos then TW will automatically import the images as svg.
In case you are linking them from external folder then
1. Open an excel sheet
2. Add details of the tiddlers with links to the images in the text field
3. Drop the excel sheet into TW using xslt plugin
Atul