Than:
- One directory name AAA Photos in the root of the USB keys
- In the sub dir of AA photos, each directory is the device with directory name of the device
- The sub dir of example Ipad will be the date of the backup
This way you should not be confuse with all these cool photos.
Don't forget to copy all the content of USB key 1 in USB key 2 each time you add some new photos.
And wait for my program when I'll be more strong to do it automatically :)