I created an exact copy of a bootable USB drive using the dd command (which is an extremely cool tool by the way) using the following command:
dd if=/dev/sdb of=myFile.img
After that, to mount it, you can simply use the kpartx command, as follows:
sudo kpartx -a myFile.img
sudo mount /dev/mapper/loop0p1 hobba -o loop,ro
where loop0p1 is the first partition, loop0p2 will be the second partition, and so on.