How do you put an image file in a json object?

I can think of doing it in two ways:


Storing the file in file system in any directory (say dir1) and renaming it which ensures that the name is unique for every file (may be a timestamp) (say xyz123.jpg), and then storing this name in some DataBase. Then while generating the JSON you pull this filename and generate a complete URL (which will be )and insert it in the JSON.


Base 64 Encoding, It's basically a way of encoding arbitrary binary data in ASCII text. It takes 4 characters per 3 bytes of data, plus potentially a bit of padding at the end. Essentially each 6 bits of the input is encoded in a 64-character alphabet. The "standard" alphabet uses A-Z, a-z, 0-9 and + and /, with = as a padding character. There are URL-safe variants. So this approach will allow you to put your image directly in the MongoDB, while storing it Encode the image and decode while fetching it, it has some of its own drawbacks:

  • base64 encoding makes file sizes roughly 33% larger than their original binary representations, which means more data down the wire (this might be exceptionally painful on mobile networks)
  • data URIs aren’t supported on IE6 or IE7.
  • base64 encoded data may possibly take longer to process than binary data.


Converting Image to DATA URI

A.) Canvas

Load the image into an Image-Object, paint it to a canvas and convert the canvas back to a dataURL.

function convertToDataURLviaCanvas(url, callback, outputFormat){
    var img = new Image();
    img.crossOrigin = 'Anonymous';
    img.onload = function(){
        var canvas = document.createElement('CANVAS');
        var ctx = canvas.getContext('2d');
        var dataURL;
        canvas.height = this.height;
        canvas.width = this.width;
        ctx.drawImage(this, 0, 0);
        dataURL = canvas.toDataURL(outputFormat);
        canvas = null; 
    img.src = url;


convertToDataURLviaCanvas('', function(base64Img){
    // Base64DataURL

Supported input formats image/png, image/jpeg, image/jpg, image/gif, image/bmp, image/tiff, image/x-icon, image/svg+xml, image/webp, image/xxx

B.) FileReader

Load the image as blob via XMLHttpRequest and use the FileReader API to convert it to a data URL.

function convertFileToBase64viaFileReader(url, callback){
    var xhr = new XMLHttpRequest();
    xhr.responseType = 'blob';
    xhr.onload = function() {
      var reader  = new FileReader();
      reader.onloadend = function () {
    };'GET', url);

This approach

  • lacks in browser support
  • has better compression
  • works for other file types as well.


convertFileToBase64viaFileReader('', function(base64Img){
    // Base64DataURL


The JSON format can contain only those types of value:

  • string
  • number
  • object
  • array
  • true
  • false
  • null

An image is of the type "binary" which is none of those. So you can't directly insert an image into JSON. What you can do is convert the image to a textual representation which can then be used as a normal string.

The most common way to achieve that is with what's called base64. Basically, instead of encoding it as 1 and 0s, it uses a range of 64 characters which makes the textual representation of it more compact. So for example the number '64' in binary is represented as 1000000, while in base64 it's simply one character: =.

There are many ways to encode your image in base64 depending on if you want to do it in the browser or not.

Note that if you're developing a web application, it will be way more efficient to store images separately in binary form, and store paths to those images in your JSON or elsewhere. That also allows your client's browser to cache the images.