diff --git a/src/openalpr/textdetection/textcontours.cpp b/src/openalpr/textdetection/textcontours.cpp
index 8f4e80c..9f022b4 100644
--- a/src/openalpr/textdetection/textcontours.cpp
+++ b/src/openalpr/textdetection/textcontours.cpp
@@ -102,14 +102,14 @@ namespace alpr
     }
   }
 
-  Mat TextContours::drawDebugImage() {
+  Mat TextContours::drawDebugImage() const {
 
       Mat img_contours = Mat::zeros(Size(width, height), CV_8U);
 
       return drawDebugImage(img_contours);
   }
 
-  Mat TextContours::drawDebugImage(Mat baseImage) {
+  Mat TextContours::drawDebugImage(Mat baseImage) const {
       Mat img_contours(baseImage.size(), CV_8U);
       baseImage.copyTo(img_contours);
 
diff --git a/src/openalpr/textdetection/textcontours.h b/src/openalpr/textdetection/textcontours.h
index 30454dc..1935bb3 100644
--- a/src/openalpr/textdetection/textcontours.h
+++ b/src/openalpr/textdetection/textcontours.h
@@ -47,8 +47,8 @@ namespace alpr
     std::vector<bool> getIndicesCopy();
     void setIndices(std::vector<bool> newIndices);
 
-    cv::Mat drawDebugImage();
-    cv::Mat drawDebugImage(cv::Mat baseImage);
+    cv::Mat drawDebugImage() const;
+    cv::Mat drawDebugImage(cv::Mat baseImage) const;
 
   private: