diff --git a/core/sample-vpImageConvert-6.cpp b/core/sample-vpImageConvert-6.cpp
index 1d851e5..ae1de1e 100644
--- a/core/sample-vpImageConvert-6.cpp
+++ b/core/sample-vpImageConvert-6.cpp
@@ -2,9 +2,13 @@
 #include <visp3/core/vpImageConvert.h>
 #include <visp3/io/vpImageIo.h>
 
+#if defined(HAVE_OPENCV_IMGCODECS)
+#include <opencv2/imgcodecs.hpp>
+#endif
+
 int main()
 {
-#if defined(VISP_HAVE_OPENCV) && (VISP_HAVE_OPENCV_VERSION >= 0x020100)
+#if defined(VISP_HAVE_OPENCV) && (VISP_HAVE_OPENCV_VERSION >= 0x020100) && defined(HAVE_OPENCV_IMGCODECS)
   vpImage<unsigned char> Ig; // A greyscale image
   cv::Mat Ip;
 
@@ -12,7 +16,7 @@ int main()
   vpImageIo::readPGM(Ig, "image.pgm");
   // Convert the vpImage<unsigned char> in to greyscale cv::Mat
   vpImageConvert::convert(Ig, Ip);
-  // Treatments on cv::MatIp
+  // Treatments on cv::Mat Ip
   //...
   // Save the cv::Mat on the disk
   cv::imwrite("image.pgm", Ip);
diff --git a/core/sample-vpImageConvert-7.cpp b/core/sample-vpImageConvert-7.cpp
index e7c6452..cf045ff 100644
--- a/core/sample-vpImageConvert-7.cpp
+++ b/core/sample-vpImageConvert-7.cpp
@@ -2,9 +2,13 @@
 #include <visp3/core/vpImageConvert.h>
 #include <visp3/io/vpImageIo.h>
 
+#if defined(HAVE_OPENCV_IMGCODECS)
+#include <opencv2/imgcodecs.hpp>
+#endif
+
 int main()
 {
-#if defined(VISP_HAVE_OPENCV) && (VISP_HAVE_OPENCV_VERSION >= 0x020100)
+#if defined(VISP_HAVE_OPENCV) && (VISP_HAVE_OPENCV_VERSION >= 0x020100) && defined(HAVE_OPENCV_IMGCODECS)
   vpImage<unsigned char> Ig; // A greyscale image
   cv::Mat Ip;
 
diff --git a/core/sample-vpImageConvert-8.cpp b/core/sample-vpImageConvert-8.cpp
index 41c0a61..c277c18 100644
--- a/core/sample-vpImageConvert-8.cpp
+++ b/core/sample-vpImageConvert-8.cpp
@@ -2,9 +2,13 @@
 #include <visp3/core/vpImageConvert.h>
 #include <visp3/io/vpImageIo.h>
 
+#if defined(HAVE_OPENCV_IMGCODECS)
+#include <opencv2/imgcodecs.hpp>
+#endif
+
 int main()
 {
-#if defined(VISP_HAVE_OPENCV) && (VISP_HAVE_OPENCV_VERSION >= 0x020100)
+#if defined(VISP_HAVE_OPENCV) && (VISP_HAVE_OPENCV_VERSION >= 0x020100) && defined(HAVE_OPENCV_IMGCODECS)
   vpImage<unsigned char> Ig; // A grayscale image
   cv::Mat Ip;
 
diff --git a/core/sample-vpImageConvert-9.cpp b/core/sample-vpImageConvert-9.cpp
index 133d173..6765473 100644
--- a/core/sample-vpImageConvert-9.cpp
+++ b/core/sample-vpImageConvert-9.cpp
@@ -2,9 +2,14 @@
 #include <visp3/core/vpImageConvert.h>
 #include <visp3/io/vpImageIo.h>
 
+
+#if defined(HAVE_OPENCV_IMGCODECS)
+#include <opencv2/imgcodecs.hpp>
+#endif
+
 int main()
 {
-#if defined(VISP_HAVE_OPENCV) && (VISP_HAVE_OPENCV_VERSION >= 0x020100)
+#if defined(VISP_HAVE_OPENCV) && (VISP_HAVE_OPENCV_VERSION >= 0x020100) && defined(HAVE_OPENCV_IMGCODECS)
   vpImage<vpRGBa> Ic; // A color image
   cv::Mat Ip;