rocket.js

Array.from(document.querySelectorAll('.message'))
        .map(message => message.querySelector('.body'))
        .forEach(message => {
            message.innerHTML = message.innerHTML.split(/ /).map(function (part, index) {
                if (part && part.length && part.length > 0) {
                    var codeMatch = part.match(/(?:```(\w*)[\n ]?([\s\S]*?)```+?)|(?:`(?:[^`]+)`)/);
                    var imgHrefMatch = part.match(/href=/i);
                    if (!codeMatch && !imgHrefMatch) {
                        return part.replace(/(https?:\/\/.*\.(?:png|jpeg|jpg|gif))/i, '<img src="$1" />');
                    } else {
                        return part;
                    }
                }
            }).join(' ');
        })