Add padding to images to get them into the same shape

You can use:

image = cv2.copyMakeBorder(src, top, bottom, left, right, borderType)

Where src is your source image and top, bottom, left, right are the padding around the image.

You can use max(sizes) – size value of the image in a while loop to add the padding to each image.
The bordertype can be one of these:

• cv2.BORDER_CONSTANT
• cv2.BORDER_REFLECT
• cv2.BORDER_REFLECT_101
• cv2.BORDER_DEFAULT
• cv2.BORDER_REPLICATE
• cv2.BORDER_WRAP

cv2.copyMakeBorder tutorial