To classify images into categories, you generate a histogram of visual word occurrences that represent an image. These histograms, called a bag of visual words, are used to train an image category classifier. You can also use the Computer Vision Toolbox™ functions to search by image, also known as a content-based image retrieval (CBIR) system. CBIR systems are used to retrieve images from a collection of images that are similar to a query image.
Interactively label rectangular ROIs for object detection, pixels for semantic segmentation, and scenes for image classification.