The TargetTabWidget::imageCallback function (in moveit_calibration_gui/handeye_calibration_rviz_plugin/src/handeye_target_widget.cpp) creates a new target object every time it is called. Since the target initialization generates some info messages, this ends up spamming the terminal. I'll have to look into it further, but it seems unnecessary to recreate the target with each image--it's probably sufficient to verify that it has been created, and to only re-initialize if the parameters change.