Tesseract.js is a JavaScript Optical Character Recognition (OCR) library based on the world's most popular OCR engine, enabling easy use both client-side and server-side with Node.js. Currently, Tesseract.js only works with local images, but it can be used to download remote images from a URL and then perform OCR on them using a combination of Node.js and the request package. The process involves downloading the image from a URL, saving it locally, and then using Tesseract.js to recognize the text in the image, which can be achieved with just 15 lines of JavaScript code.