Amazon is building a point-of-sale system based on the Kindle Fire that it will offer to merchants, according to a new report. The Wall Street Journal reports that the Kindle checkout system, which could be available as early as this summer, will let brick-and-mortar retailers ring up customers' purchases using a Kindle in conjunction with a credit-card reader.

The system is reportedly being built by former engineers at the San Francisco startup GoPago, which was acquired by DoubleBeam last month. As the Journal notes, Amazon's entry into the world of physical retail would give it a chance to mine data on the shopping habits of customers in stores, where 90 percent of business still takes place. It comes at a time when Apple is said to be pursuing a mobile payments service of its own.

Getting merchants to adopt such a system will be difficult

But getting merchants to adopt such a system will be difficult, if not impossible. Square, which makes a point-of-sale system of its own tied to Apple's iPad, has struggled to attract other national retailers after signing a deal with Starbucks in 2012. The costs and employee re-training required to switch away from traditional checkout systems, such as those made by VeriFone and NCR Corp., can be prohibitive.

That's why Amazon plans start by offering the system to smaller retailers, according to the Journal, which says Amazon might still abandon the project. In an effort to win their business, Amazon has considered offering help with website development, data analysis, and promotions, the report said.

An Amazon spokeswoman declined to comment.