Google Cloud Vision API comprises various complex and powerful machine learning models that help to perform image analysis. It classifies images into various categories using an easy-to-use REST API. The important features provided by Google Cloud Vision include the following:

• Label detection: This enables us to classify images into thousands of categories. The images can be categorized into various common category labels, such as animals and fruits.
• Image attribute detection: This enables us to detect individual objects from within images. It can also detect attributes such as prominent color.
• Face detection: This enables us to detect faces from within images. If there are multiple faces in the images, each can be detected individually. It can also detect the prominent attributes associated with a face, such as wearing a helmet.
• Logo detection: This enables us to detect printed words from images. Prominent logos are trained which can be detected.
• Landmark detection: It is trained to detect prominent landmarks – natural and man-made–so these are detected through Google Vision.
• Optical character recognition: This helps to detect the text within images even if they aren't in English. This supports a wide range of languages.
• Explicit content detection: This helps to identify the type of content or sentiment of the content, such as violent or humorous. It enables us to perform sentiment analysis of images by leveraging the metadata information that can be built.
• Search web: This searches the web for similar images.

All these features provided by Google Cloud Vision can be used by invoking simple RESTful APIs provided by Google. However, for their use, there is a price attached to using each feature. A combination of features can also be used. The pricing details can be found on the Google Cloud Vision website: https://cloud.google.com/vision/.