Product owners often rely on design patents for protection against infringement by copycats. But they often also ask how similar or different does the knock off have to be in order to be covered or not covered by the design patent.
Unfortunately, there is no clear dividing line between design patent infringement and no infringement. And there is also no quantitative rule that says how much similarity or dissimilarity is needed for infringement.
In one example - Super-Sparkly v. Skyline, the design patent covered a pepper spray canister with rhinestones on the bottom. The device accused of infringement did not have rhinestones on the bottom. The court found no infringement.
In legalese, design infringement is decided on whether the accused product appears "substantially the same" as the patented design. That is judged by an "ordinary observer."
Under the "ordinary observer" test, there is no infringement if the accused product and patented design are "sufficiently distinct" and "plainly dissimilar."
You are likely thinking to yourself that these legal tests are not helpful. And you may be right.
But, in the above example, one may agree that removing the rhinestones from the bottom of the cannister may be a significant difference - even if the overall shape of the cannisters were similar.