The OpenCV documentation itself is good to start with.
https://opencv-python-tutroals.readthedocs.io/en/latest/py_tutorials/py_imgproc/py_table_of_contents_imgproc/py_table_of_contents_imgproc.html

image = Image.open('demo_image.jpg')
new_image = image.resize((400, 400))
new_image.save('image_400.jpg')
print(image.size) # Output: (1920, 1280)
print(new_image.size) # Output: (400, 400)

# The file format of the source file.
print(image.format) # Output: JPEG
# The pixel format used by the image. Typical values are "1", "L", "RGB", or "CMYK."
print(image.mode) # Output: RGB
# Image size, in pixels. The size is given as a 2-tuple (width, height).
print(image.size) # Output: (1920, 1280)
# Colour palette table, if any.
print(image.palette) # Output: None