How different should a product need to be to be marketable without infringing on a patent?

This is an excellent question. The first step is to determine whether or not the person marketing the "do it yourself photobooths" is operating under a patent. The patent could be assigned to the company or licensed to the company. Or, there could be a pending patent application. The person may have the product marked with one or more patent numbers or simply "patent pending". Once a patent has been identified, an attorney needs to review the claims of the patent to determine the scope of the patent. It may be relatively easy to design around the patent. This all is highly technical and it is strongly advised that you seek the assistance of counsel. If there is no issued patent or "patent pending", the technology may be in the public domain and available to anyone. Good Luck!!

There is not a simple answer to this question. Answering that question requires that an attorney review the patent(s) in question, including their file histories and then discuss their scope with you while exploring how you might do it differently to not infringe. Plan on spending at least between about $500 - $1500+ on this process.

First you will need to determine if any part of the other product has been and still is patented. Using your example, there probably aren't very many, if any, elements of a photo booth that are under patent protection. However, the inventor may have gotten a "design" patent because of some unique way the photo booth is structured or appears. If that's the case, you will have to come up with a different design to avoid infringement. If there is a utility patent, you will have to avoid the parts of the photo booth that are covered by it when you develop yours.

To avoid infringement charges - the product should be different enough that a jury won't believe that the patent covers it. Patents have "claims" that define the scope and coverage of the invention. These come at the end of the patent - and get interpreted by a judge in Federal Court as to what they mean and what they cover. Broad claims capture numerous differences between the claimed invention and the accused product. Narrow claims capture only products that are closely or exactly as defined by the claims of the patent. There are two types of patent infringement - (1) literal infringement and (2) infringement under the doctrine of equivalents (DOE). If a patent claim defines your product exactly - literal infringement will likely be found by the court. If the patent claim does not literally define your product - but instead, your product does the same thing, in the same was, and achieves the same result as the claimed invention - DOE infringement will likely be found. There are specific rules regarding the analysis of claims and products - if you leave out a necessary claim element from your invention, and do not replace it with an equivalent element - you may not infringe the claim under the "all elements rule." To be safe - see a patent attorney to compare your product to the patent. This is a called freedom to operate analysis.