set IMAGE_PATH

in order to allow that documentation includes images

cmake/Doxyfile.in

@@ -956,7 +956,7 @@ EXAMPLE_RECURSIVE      = NO
 # that contain images that are to be included in the documentation (see the
 # \image command).
 
-IMAGE_PATH             =
+IMAGE_PATH             = @CMAKE_CURRENT_SOURCE_DIR@
 
 # The INPUT_FILTER tag can be used to specify a program that doxygen should
 # invoke to filter for each input file. Doxygen will invoke the filter program