How re-image a Mac Hard Drive using Disk Utility

1st step is to put the mac that you are trying to re-image into target mode by pressing and holding T while it is turning on or go to system preferences and choose START UP DISK then click on the lock enter your administrator password and click on Target Disk Mode.

2nd step connect the firewire or thunderbolt cables to both macs

 

3rd Step is to open Disk Utility on your mac that is not in target disk mode to do that you need to open finder and applications then find the folder utilities, after you found utilities then double-click Disk Utility or click on the desktop and press command+shift+U 

Now that you have disk utility open you see your other Mac's HD (Hard Drive) If you are using Mac OS X 10.10 or lower you disk utility will look like this:

If it looks like this then you need to click restore and put the disk image in the first bar and the other Mac's HD in the second but it you use Mac OS X 10.11 or later then Disk Utility will look like this:

If it looks like this then you need to click on the hard drive and go to the menu bar at the top of the screen and click on EDIT and then choose RESTORE or do the keyboard shortcut Command + Shift + R and choose the Disk image from there