Merge pull request #23108 from crackwitz:issue-23107

Usage of imread(): magic number 0, unchecked result

* docs: rewrite 0/1 to IMREAD_GRAYSCALE/IMREAD_COLOR in imread()

* samples, apps: rewrite 0/1 to IMREAD_GRAYSCALE/IMREAD_COLOR in imread()

* tests: rewrite 0/1 to IMREAD_GRAYSCALE/IMREAD_COLOR in imread()

* doc/py_tutorials: check imread() result

samples/python/calibrate.py

@@ -57,7 +57,7 @@ def main():
 
     def processImage(fn):
         print('processing %s... ' % fn)
-        img = cv.imread(fn, 0)
+        img = cv.imread(fn, cv.IMREAD_GRAYSCALE)
         if img is None:
             print("Failed to load", fn)
             return None

samples/python/mouse_and_match.py

@@ -69,7 +69,7 @@ class App():
             if ext == "png" or ext == "jpg" or ext == "bmp" or ext == "tiff" or ext == "pbm":
                 print(infile)
 
-                img = cv.imread(infile,1)
+                img = cv.imread(infile, cv.IMREAD_COLOR)
                 if img is None:
                     continue
                 self.sel = (0,0,0,0)