diff --git a/cmake/OpenCVFindLibsGrfmt.cmake b/cmake/OpenCVFindLibsGrfmt.cmake
index 9a1b9d01c2..4523f39c89 100644
--- a/cmake/OpenCVFindLibsGrfmt.cmake
+++ b/cmake/OpenCVFindLibsGrfmt.cmake
@@ -45,6 +45,11 @@ else()
   endif()
 
   if(NOT ZLIB_FOUND)
+    if(NOT BUILD_ZLIB)
+      message(WARNING "ZLIB library has not been found, falling back to built-in version. "
+              "Set ZLIB_ROOT or ZLIB_DIR variable so that find_package(ZLIB) would be able to find it. "
+              "See find_package and FindZLIB cmake documentation for details.")
+    endif()
     ocv_clear_vars(ZLIB_LIBRARY ZLIB_LIBRARIES ZLIB_INCLUDE_DIR)
 
     set(ZLIB_LIBRARY zlib CACHE INTERNAL "")
@@ -83,6 +88,12 @@ if(WITH_JPEG)
   endif()
 
   if(NOT JPEG_FOUND)
+    if(NOT BUILD_JPEG)
+      message(WARNING "JPEG library has not been found, falling back to built-in version. "
+              "Add the external installation prefix to CMAKE_PREFIX_PATH, or set JPEG_INCLUDE_DIR "
+              "and JPEG_LIBRARY, so that FindJPEG can locate it. "
+              "See FindJPEG cmake documentation for details.")
+    endif()
     ocv_clear_vars(JPEG_LIBRARY JPEG_INCLUDE_DIR)
 
     if(NOT BUILD_JPEG_TURBO_DISABLE)
@@ -153,6 +164,12 @@ if(WITH_TIFF)
   endif()
 
   if(NOT TIFF_FOUND)
+    if(NOT BUILD_TIFF)
+      message(WARNING "TIFF library has not been found, falling back to built-in version. "
+              "Add the external installation prefix to CMAKE_PREFIX_PATH, or set TIFF_INCLUDE_DIR "
+              "and TIFF_LIBRARY, so that FindTIFF can locate it. "
+              "See FindTIFF cmake documentation for details.")
+    endif()
     ocv_clear_vars(TIFF_LIBRARY TIFF_LIBRARIES TIFF_INCLUDE_DIR)
 
     set(TIFF_LIBRARY libtiff CACHE INTERNAL "")
@@ -201,6 +218,11 @@ endif()
 if(WITH_WEBP AND NOT WEBP_FOUND
     AND (NOT ANDROID OR HAVE_CPUFEATURES)
 )
+  if(NOT BUILD_WEBP)
+    message(WARNING "WebP library has not been found, falling back to built-in version. "
+            "Set WEBP_INCLUDE_DIR and WEBP_LIBRARY, or add the external installation prefix to "
+            "CMAKE_PREFIX_PATH, so that the external WebP can be located.")
+  endif()
   ocv_clear_vars(WEBP_LIBRARY WEBP_INCLUDE_DIR)
   set(WEBP_LIBRARY libwebp CACHE INTERNAL "")
   set(WEBP_LIBRARIES ${WEBP_LIBRARY})
@@ -353,6 +375,11 @@ if(NOT HAVE_SPNG AND WITH_PNG)
   endif()
 
   if(NOT PNG_FOUND)
+    if(NOT BUILD_PNG)
+      message(WARNING "PNG library has not been found, falling back to built-in version. "
+              "Set PNG_ROOT or PNG_DIR variable so that find_package(PNG) would be able to find it. "
+              "See find_package and FindPNG cmake documentation for details.")
+    endif()
     ocv_clear_vars(PNG_LIBRARY PNG_LIBRARIES PNG_INCLUDE_DIR PNG_DEFINITIONS)
 
     set(PNG_LIBRARY libpng CACHE INTERNAL "")