If you are looking for an easy reliable solution to use in your project, here are 10 useful libraries that can work in all modern browsers and will add options to annotate the web.

Annotorious

A JavaScript image annotation library. Add drawing, commenting and labeling functionality to images in Web pages with just a few lines of code.

Annotator

Annotator is an open-source JavaScript library to easily add annotation functionality to any webpage. Annotations can have comments, tags, links, users, and more. Annotator is designed for easy extensibility so its a cinch to add a new feature or behaviour. Annotator also fosters an active developer community with contributors from four continents, building 3rd party plugins allowing the annotation of PDFs, EPUBs, videos, images, sound, and more.

Chartjs Plugin Annotation

Annotation plugin for Chart.js. This plugin draws lines, boxes, points and ellipses on the chart area. Annotations work with line, bar, scatter and bubble charts that use linear, logarithmic, time, or category scales. Annotations will not work on any chart that does not have exactly two axes, including pie, radar, and polar area charts.

React Image Annotation

An infinitely customizable image annotation library built on React.

React PDF Highlighter

react-pdf-highlighter is a React library that provides annotation experience for PDF documents on web. It is built on top of PDF.js by Mozilla. Text and rectangular highlights are supported. Highlight data format is independent of the viewport, making it suitable for saving on the server.

Videojs Annotation Comments

A plugin for video.js to add support for timeline moment/range comments and annotations.

React Image Annotate

Powerful React component for image annotations with bounding boxes, tagging, classification, multiple images and polygon segmentation.

D3 Annotation

Use d3-annotation with built-in annotation types, or extend it to make custom annotations. It is made for d3-v4 in SVG.

TextAnnotator

Small and simple JS tool for making powerful underline, highlight and strike text annotations.

Mirador

An open-source, web-based ‘multi-up’ viewer that supports zoom-pan-rotate functionality, ability to display/compare simple images, and images with annotations.