实现效果

LetterAvatar的原理就是利用了浏览器对象canvas

在线体验：https://mouday.github.io/tools/pages/letter-avatar/index.html

LetterAvatar.js 完整代码

/*
 * LetterAvatar
 * 
 * Artur Heinze
 * Create Letter avatar based on Initials
 * based on https://gist.github.com/leecrossley/6027780
 */
(function(w, d){
    function LetterAvatar (name, size, color) {

        name  = name || '';
        size  = size || 60;

        var colours = [
                "#1abc9c", "#2ecc71", "#3498db", "#9b59b6", "#34495e", "#16a085", "#27ae60", "#2980b9", "#8e44ad", "#2c3e50", 
                "#f1c40f", "#e67e22", "#e74c3c", "#ecf0f1", "#95a5a6", "#f39c12", "#d35400", "#c0392b", "#bdc3c7", "#7f8c8d"
            ],

            nameSplit = String(name).split(' '),
            initials, charIndex, colourIndex, canvas, context, dataURI;


        if (nameSplit.length == 1) {
            initials = nameSplit[0] ? nameSplit[0].charAt(0):'?';
        } else {
            initials = nameSplit[0].charAt(0) + nameSplit[1].charAt(0);
        }

        if (w.devicePixelRatio) {
            size = (size * w.devicePixelRatio);
        }
            
        charIndex     = (initials == '?' ? 72 : initials.charCodeAt(0)) - 64;
        colourIndex   = charIndex % 20;
        canvas        = d.createElement('canvas');
        canvas.width  = size;
        canvas.height = size;
        context       = canvas.getContext("2d");
         
        context.fillStyle = color ? color : colours[colourIndex - 1];
        context.fillRect (0, 0, canvas.width, canvas.height);
        context.font = Math.round(canvas.width/2)+"px Arial";
        context.textAlign = "center";
        context.fillStyle = "#FFF";
        context.fillText(initials, size / 2, size / 1.5);

        dataURI = canvas.toDataURL();
        canvas  = null;

        return dataURI;
    }

    LetterAvatar.transform = function() {

        Array.prototype.forEach.call(d.querySelectorAll('img[avatar]'), function(img, name, color) {
            name = img.getAttribute('avatar');
            color = img.getAttribute('color');
            img.src = LetterAvatar(name, img.getAttribute('width'), color);
            img.removeAttribute('avatar');
            img.setAttribute('alt', name);
        });
    };


    // AMD support
    if (typeof define === 'function' && define.amd) {
        
        define(function () { return LetterAvatar; });
    
    // CommonJS and Node.js module support.
    } else if (typeof exports !== 'undefined') {
        
        // Support Node.js specific `module.exports` (which can be a function)
        if (typeof module != 'undefined' && module.exports) {
            exports = module.exports = LetterAvatar;
        }

        // But always support CommonJS module 1.1.1 spec (`exports` cannot be a function)
        exports.LetterAvatar = LetterAvatar;

    } else {
        
        window.LetterAvatar = LetterAvatar;

        d.addEventListener('DOMContentLoaded', function(event) {
            LetterAvatar.transform();
        });
    }
})(window, document);

可以在浏览器中直接使用

<img width="256" height="256" avatar="Dao Lam" color="#0D8ABC">

参考文章

1. https://mkblog.cn/blog/demo/LetterAvatar/
2. https://github.com/daolavi/LetterAvatar/