This document discusses various techniques for image retrieval, including text-based, content-based, and hybrid approaches. Content-based image retrieval (CBIR) extracts visual features like color, texture, shape from images and is able to retrieve similar images to a query image. CBIR systems segment images, extract features, search databases, and return results. CBIR techniques are improving but challenges remain around reducing the semantic gap between low-level features and high-level concepts. Future areas of research include developing techniques more aligned with human perception and improving efficiency and interfaces.