title: How can I solve ` cv2.dnn.blobFromImage (frame) error for cropped images`?
body: <p><code>cv2.error: OpenCV(4.4.0) C:\Users\appveyor\AppData\Local\Temp\1\pip-req-build-71670poj\opencv\modules\dnn\src\dnn.cpp:371: error: (-215:Assertion failed) image.depth() == blob_.depth() in  function 'cv::dnn::dnn4_v20200609::blobFromImages'</code></p>
  <p>This error is raised when I run the following code:</p>
  <pre><code>crop = frame[y:y + h, x:x + w]
  img_blob = cv.dnn.blobFromImage(crop)
  </code></pre>