I plugged a flash drive into my Nexus 5 (via OTG cable) and started NMI. In the upper left of the app I tapped the NMI icon. It opens a list of options.. I choose "advanced" near the bottom. On the next screen I tapped the square icon to the left of the USB icon. In the pop up window I tapped the flash drive. This displayed the contents of the flash drive. I tapped 2 files to highlight them. Then, I tapped the down facing arrow just above the flash drive list and chose copy, then "OK" in the pop up window. This copied the files to my phone. Using my file manager app I found they were copied to the root of the phone (/storage/emulated/). It should work the same way with your memory card in a reader connected to the OTG cable. It may also work directly connecting your camera to the OTG cable. There may be a way to specify where to copy the files too but I did not find it. Hope this helps.