Convolutional Neural Networks (CNNs) are a type of deep learning algorithm that is specifically designed to work with image data. They are based on the idea of a convolution, which is a mathematical operation that is used to extract features from an image. These features are then used to classify the image or detect objects within it.

The architecture of a CNN typically includes several layers, with the first layer being the input layer. This layer takes in the image and passes it through the network. The next layer is the convolutional layer, which applies a set of filters to the image. These filters are used to detect specific features in the image, such as edges or textures. The number of filters and their size can be defined by the user, depending on the complexity of the dataset.

After the convolutional layer, the image is passed through a pooling layer, which is used to reduce the spatial dimensions of the image. This is done to reduce the computational complexity of the network and also to make the network more robust to small translations of the image. The most common pooling method is max pooling, which takes the maximum value from a certain window in the image.

The next layer is the fully connected layer, which is used to make the final prediction. This layer takes the output of the previous layers and uses it to classify the image or detect objects within it. The fully connected layer is also called the dense layer, in which each neuron is connected to all the neurons in the previous layer.

One of the key advantages of CNNs is that they can learn to detect features in images without the need for any prior information about the image. This is known as unsupervised learning. This allows CNNs to be trained on large datasets of images and can improve the accuracy of the network over time.

Let's take an example of how to implement a simple CNN for image classification in python. The first step is to import the necessary libraries.

import numpy as np
import keras
from keras.datasets import cifar10
from keras.models import Sequential
from keras.layers import Dense, Dropout, Flatten, Conv2D, MaxPooling2D

Next, we will load the CIFAR-10 dataset, which consists of 60,000 32x32 color images in 10 classes, with 6,000 images per class. There are 50,000 training images and 10,000 test images.

(x_train, y_train), (x_test, y_test) = cifar10.load_data()

Now we will preprocess the data by normalizing the pixel values and one-hot encoding the labels.

x_train = x_train.astype('float32')
x_test = x_test.astype('float32')
x_train /= 255
x_test /= 255

y_train = keras.utils.to_categorical(y_train, 10)
y_test = keras.utils.to_categorical(y_test, 10)

Now we can define our CNN model. We will use a stack of convolutional and max pooling layers followed by a dense layer for classification.

model = Sequential()
model.add(Conv2D(32, (3, 3), activation='relu', input_shape=(32, 32, 3)))