There are no requirements, and I've never heard of countries "being official members of ROS". That would be strange as well, as 'ROS' is a software framework.
As to the image you show: that is the user map as of December 2013, which is rather old, and was made based on user contributed data (so only people / institutions / companies that happened to tell others they were using ROS are shown on it).
For a more up-to-date version, see the ROS Users of the World map that @DLu maintains. It already has one dot for Peru: San Pablo Catholic University.
Note that that map is also based on user input: just submit a Pull Request to DLu/ros_map to get included.
Summary: you don't need to belong to some "ROS club" to be considered a ROS user. Just using it is enough. If you want to show others that you are using it, then you could consider contributing to the ROS Map (linked above).
Originally posted by gvdhoorn with karma: 86574 on 2017-07-31
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