I think this will help, Base64 is addressed by CSS in a different way, you should set the data type of the image to base64, this will help the CSS to change the base64 to image and display it to the user. and you can use this from javascript by assigning the background image using the jquery script, it will automatically change the base64 to mage and display it
url = "data:image;base64,"+data.replace(/(\r\n|\n|\r)/gm, "");_x000D_
$("body").css("background-image", "url('" + url.replace(/(\r\n|\n|\r)/gm, "") + "')");
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