Dump/Restore partition table

sfdisk -d /dev/sdX > ptable # Dump to file ptable
cat ptable | sfdisk /dev/sdX # Restore from file ptable
sfdisk -d /dev/sdX | sfdisk /dev/sdY # Copy to another disk

Create a disk image

dd if=/dev/sdX of=disk_image.img

where sdX is the disk name (sda, sdb etc)

Create a partition image

dd if=/dev/sdXn of=partition_image.img

where sdXn is the partition name (sda1, sdc4 etc)

Mount a partition from a disk image

get partition table fro mdisk image

fdisk -l disk_image.img
 
Disk disk_image.img: 500.1 GB, 500104826880 bytes
255 heads, 63 sectors/track, 60800 cylinders, total 976767240 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x4e19293b
 
         Device Boot      Start         End      Blocks   Id  System
disk_image.img1   *        2048      206847      102400    7  HPFS/NTFS/exFAT
disk_image.img2          206848   102399999    51096576    7  HPFS/NTFS/exFAT
disk_image.img3       102400000   961781109   429690555   83  Linux
disk_image.img4       961781110   976751999     7485445   82  Linux swap / Solaris

determine partition offset as follows: sector_size * start_sector

For 3rd partition (disk_image.img3) this would be 512 * 102400000

mount -o loop,offset=$((512*102400000)) disk_image.img /mnt

Copy a partition from a disk image

Determine partition size and offset as above

dd if=disk_image.img of=/dev/sdXn bs=512 skip=$((102400000)) count=$((961781109-102400000+1))