Expanding on Frank's spot-on response: _my suggestion_ is to use Time Machine as an _auxiliary_ back-up, but not as a primary back-up. Institute a rigorous 3-copies back-up program*, and rely on TM to have your back in case of (quite common) human or machine failure.
*one working copy, and two back-up copies. Never have all three in the same physical location.
Drives are cheap. Buy them in duplicate for Libraries that are on your system drive, and triplicate for Libraries on external drives. Use SuperDuper or CarbonCopyCloner to keep _two_ copies of your working Library _and your Referenced Originals_ current. Never have all three copies in the same physical location. And use TM as a last resort in case those fail.
Note, too, that Time Machine provide more versioning back-up than SuperDuper or any cloning system.
I recommend _not_ relying on only TM or only a cloning system. TM works well and is close to cost-free (use an EHD that is too slow for regular work). SuperDuper (and others) work well and cost some money (but, suffice it to say, far far far far far less than the cost of acquiring and developing your Image data). Together they provide a reasonable -- to me -- level of security.
Message was edited by: Kirby Krieger