• First you need to have an access to the system, in other words you have to log into the system. If you don't have the user password, you must find a way to find it. When you are logged in the system, you need to generate the bitlocker-key. These devices are automatically protected with bitlocker when you register the system the first time with your Windows live account. You'll need the key to unencrypt your image file.

• Then, when the OS is booted, hold on the left shift-key and click on reboot

• You should see the advanced options menu

• Click on Troubleshoot -- > Advanced Options -- > Command prompt

• If everything's worked fine a command prompt should appear. That's it, now you can use the command dism to make a volume disk image.

• If needed you can use diskpart to assign a letter to the hidden volumes/other partitions.

• Use the command Diskpart -- > list volume -- > select volume X -- > assign letter=X

• Ok now that every volume is assigned, now you can use the command DISM
  (DISM Image Management command line options)
  

dism /capture-image /imagefile:X:"yourimagefile".WIM /capturedir:c:\ /name:winrt

/imagefile : choose the path and the name of the file you want to create /capturedir : choose the volume you want to copy /name : choose a label

• Now that the primary volume is copied, you can append the hidden volumes to your image.
• Use the command

dism /append-image /imagefile:X:"yourimagefile" /capturedir:d:\ /name:system

• You have now a .wim file !
• Copy your Wim file on your work computer.
• Open a command prompt and use the dism command again.
• You need to "mount" your file to extract the files on your computer.
• First type

dism /get-wiminfo /wimfile:X:"path to your wim file"

• Normally you should see the different partitions that you have imaged, each one corresponding to an index.
• Type now the following command

"dism /mount-wim /wimfile:X:"path to your wim file" /index:X /mountdir:X:\path to extract the files"

/index: choose the number of the index (volume) you want to extract /mountdir: choose the directory where to extract the files

• Once finished to unmount type the following command

dism /unmount-wim /mountdir:X:"path to your wim file" /discard

(source)