We will start with a small dataset that was collected especially for this book. It has three classes: buildings, natural scenes (landscapes), and pictures of text. There are 30 images in each category, and they were all taken using a cell phone camera with minimal composition. The images are similar to those that would be uploaded to a modern website by users with no photography training. This dataset is available in the companion code repository. Later in this chapter, we will look at a larger dataset with more images and more categories that are more difficult to classify.
When classifying images, we start with a large rectangular array of numbers (pixel values). Nowadays, millions of pixels are common. We could try to feed all these numbers as features into the learning algorithm. This is not a very good idea unless you have a lot of data. This is...
