In this step we create a file tag that accepts only images and it calls preview_image() function with the change event as a parameter when user choose image from folder.In preview() function we first create FileReader object to get the file data and then when the reader is loaded we create a function to get the output image and change its source to result and then we use readAsDataURL to preview the image.You may also like jQuery live preview. Thats all, this is how to preview image before upload using JavaScript, CSS and HTML.You can customize this code further as per your requirement. And please feel free to give comments on this tutorial.