No photos to import
I'm trying to import some JPEG files into Photos on an iPad mini 3 running iOS 10.2. I copied the photos to the top level of a 2GB SD card using a Mac. I connected the SD card to an IOGear USB card reader and plugged a USB cable from that via a Lightning to USB Camera Adapter to the iPad. Photos launches on the iPad and the Import tab activates, but it tells me that there are "No photos to import". How can I get this to work? Do I need to have the data structure on the SD card that a camera SD card would have? Thanks for any advice.
MacBook Air, macOS Sierra (10.12.1)