This little script removes images which appear to be in the portrait format (tweak it for your own needs).
#!/bin/bash
orientation=`exiftool -orientation "$1"` echo "$1" has $orientation; if ! [[ $orientation =~ "Horizontal" ]] then
echo "so removed"; rm "$1";
fi
You can run it recursively with:
find directory/ -name "*.JPG" -exec ./rm-portrait {} \;