Are your images sysprepped or are you imaging a working machine without this? If the latter, then your problem is caused by the fact that the computer's password on the server gets changed every seven days and so if you restore an image that is more than seven days old (it may be less depending on where in the cycle you reimage), the domain no longer recognises the old computer account password and so it cannot connect back to the domain.
There is a registry key that turns off the computer account password change:
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\Netlogon\Parameters\DisablePasswordChange
Change this DWORD value from 0 to 1, and the password change stops - with whatever additional security risks this presents.
Note also that if the server policies have been set to ignore this local setting, then the computer password change gets forced regardless. It all depends on how "clever" your security admins are...