Preprocessing for VGG Network needed or not?

Do we need to normalise the images to pass through vgg or they get preprocessed automatically?

If yes, please suggest a preprocessing script for images which is used generally?

To my understanding you need to resize your images and normalize the colors in them to get the best results. An example is as follows.

data_transform = transforms.Compose([
    transforms.Normalize([0.485, 0.456, 0.406], [0.229, 0.224, 0.225])]), 

You would then pass this transform as a parameter for your datasets like this:

datasets.ImageFolder(path_to_training_directory, transform=data_transform)