The covers of these movies, other that a couple of the early classics, have rounded corners, if you find a square corner on a Masterpiece you know its been copied.
Robin Hood, Cinderella, Lady...Tramp, and Sleeping Beauty Classic versions have a black diamond on the top of the cover and a red diamond on the bottom.
A Masterpiece WITHOUT a hologram castle on the top front cover means it is a Limited Quantity release. The castle hologram means that these movies remain in the stores, that doesn't mean they are worthless, but they are not as collectible as the others.
An original Lady and the Tramp may have a paper label, but it for sure will have "Walt Disney Classic" printed in red ink on the black case inside the cover. Other than Lady..., there is never a paper label in the movie case. The titles are always embossed directly onto the case.
On the side of a black movie case, again other than the early Classics, you will always find embossed "BVHV" in orange or yellow. This stands for Buena Vista Home Video.
The safety tab, to prevent re-recording over, will show no evidence of remains. Originals are smooth on the bottom where others need to be broken off.
A new Disney manufactured video will have a rather large overlapping of plastic shrink-rap on the back. If your movie doesn't have this overlapping of plastic - beware of a fake.
I hope this clears up some of the mystique surrounding Disney videos as collectibles. For me and my dollar, well, I have no unopened movies, but I do have contented children. So, pop some popcorn, grab a comfortable seat, and relax in front of some of the best family entertainment to be found. And, buy a extra copy to leave unopened for an investment if you choose. Enjoy!