Linux

Check which disks are mounted in you computer:

$ df -h
S.ficheros     Tamaño Usados  Disp Uso% Montado en
/dev/sda1         26G    21G  3,7G  86% /
none             4,0K      0  4,0K   0% /sys/fs/cgroup
udev             2,0G   4,0K  2,0G   1% /dev
tmpfs            404M   960K  403M   1% /run
none             5,0M      0  5,0M   0% /run/lock
none             2,0G   220K  2,0G   1% /run/shm
none             100M    52K  100M   1% /run/user
Home             112G   103G  9,2G  92% /media/home/

Insert the SD and run again df -h, check how the new disk is named :

$ df -h
S.ficheros     Tamaño Usados  Disp Uso% Montado en
/dev/sda1         26G    21G  3,7G  86% /
none             4,0K      0  4,0K   0% /sys/fs/cgroup
udev             2,0G   4,0K  2,0G   1% /dev
tmpfs            404M   960K  403M   1% /run
none             5,0M      0  5,0M   0% /run/lock
none             2,0G   220K  2,0G   1% /run/shm
none             100M    52K  100M   1% /run/user
Home             112G   103G  9,2G  92% /media/home/
/dev/sdb1         56M    20M   37M  36% /media/inigo/boot
/dev/sdb2        3,8G   2,8G  759M  80% /media/inigo/13d368bf-6dbf-4751-8ba1-88bed06bef77

Notice that the new disk is named sdb and has two partitions sdb1 and sdb2

Now umount the SD:

umount the disk:
umount /dev/sdb1
umount /dev/sdb2

Now, flash the image in the SD:

# if you have uncompressed image:
sudo dd bs=8M if=/path/to/image/erle_image_name.img of=/dev/sdb

#if you have img.gz compressed image:
sudo zcat /path/to/image/erle_image_name.img.gz | sudo dd of=/dev/sdb bs=8M

#if you have tar.xz compressed image:
sudo xz -dkc /path/to/image/erle_image.tar.xz > /dev/sdb