diff -udHrN -- a/configure.ac b/configure.ac

--- a/configure.ac	2022-05-13 13:28:38.000000000 +0200

+++ b/configure.ac	2022-05-21 09:08:38.158557876 +0200

@@ -172,7 +172,7 @@

 			  [OPENCV_LIBS="-lopencv_core -lopencv_imgproc -lopencv_calib3d"],

 			  [PKG_CHECK_MODULES([OPENCV], [opencv4 >= 4.2.0],

 					     [AC_MSG_WARN([OpenCV 4.2 found, translation-only registration will be disabled - requires 4.4])]

-					     [OPENCV_LIBS="-lopencv_core -lopencv_imgproc -lopencv_calib3d"],

+					     [OPENCV_LIBS="-lopencv_core -lopencv_imgproc -lopencv_calib3d -lopencv_flann"],

 					     AC_MSG_ERROR([opencv not found.]))])

 else

 	AC_MSG_ERROR([no C++ compiler found])