While I think that the identical DVD covers are pretty funny, the main problem here is how bad and lacking in originality the actual movies with the imitation covers are...
Just to add to the Ghost Ship comparsion. See the movie art for Death Ship-- can't post images or links just yet, so go to allmovie.com and search for "Death Ship."
I think some of the comparisons are apt, but sometimes a studio will use a poster from one film to put a deliberate spin on the poster of another. Thus, the Problem Child poster, which was intentionally riffing on the one for Parenthood. Sort of like an anti-parenthood.
The real artwork ripoffs tend to occur down in the B-movies, as evidenced by that shot for Ghost Rig. I was recently flipping through a bargain bin in an FYE and noticed a whole bunch of B-movie and TVMovie fare that had covers similar to those for A-list releases. Maybe if more studios would go back to using actual ARTISTS to create the work, instead of just slapping gigantic side-lit photographs of star heads and groupings of sullen horror-movie teenagers, it would be a little more difiicult for the cheapo producers to rip them off.
As I'm not sure how to post images here, I'll just mention one poster where they made NO effort to disguise the original. The painted theatrical release poster for the Simon Wincer film Quigley Down Under was a near-exact duplicate of the poster from an earlier movie called Lassiter, both films starring Tom Sellect. They basically used the same design for the painting (big side-lit Selleck head, supporting character smaller in front of a circle (Alan Rickman in front of the sun in Quigley; the leading lady Whoever in front of the moon in Lassiter) and, if I recall, a gun running along side his face in both versions. From an artistic standpoint, I always loved the design of these posters, and for years kept a screener bearing that version of the Quigley art, because it didn't end up on the release tapes.
There's also a newer B-movie I've seen lately called The Hundred Mile Rule or Thousand Mile Rule or something like that and the poster is highly reminiscent of the one for the garbage remake of Gone in Sixty Seconds. There's a tonne of this crap out there.
While these aren't rip offs, rather parodies, I think this trend to redo the Conan poster (or a mutation of it) is getting a bit stale. (Is the Conan cover the fist one to use this setup?)