Cascade classier DetectMultiScale()

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So am trying to use cascade.detectMultiScale() as a classifier by using an input image of size 24*24 (the same size used in the cascade training) and the parameters:

detections= my_cascade.detectMultiScale(img, scaleFactor=1.05, minNeighbors=1, minSize=(1,1), maxSize=(24,24))

I am not getting any detections at all although I am using the same positive images used in the training to test! What is causing that!