Trying to do an un-bootable image disk backup on a re-formatted 1TB WD Passport external hard drive
If it fails on creating a disk image, then there may be one (damaged) file causing the problem.

Why not open the user folder and copy each sub-folder in turn and when you find the folder that fails copy the contents inside individually until you find the errant file... 

Of course, it may not be a personal file causing the issue...