I am running below code in google app script.
var data = "iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO9TXL0Y4OHwAAAABJRU5ErkJggg==";
var ssblob = Utilities.newBlob(data,"image/png","MyImage");
Logger.log(ssblob.getBytes().length);
Logger.log(ssblob.getName());
Logger.log(ssblob.getDataAsString());
Logger.log( ssblob.getContentType());
var ss = SpreadsheetApp.getActiveSheet();
ss.insertImage(ssblob,4,4);
Execution Log
5:34:37 PM Notice Execution started
5:34:37 PM Info 116.0
5:34:37 PM Info MyImage
5:34:37 PM Info iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO9TXL0Y4OHwAAAABJRU5ErkJggg==
5:34:37 PM Info image/png
5:34:38 PM Error
Exception: The blob format is unsupported.
newBlob(data) can only create a blob from a byteArray or a stringSample:
function myFunction() {
var data = "iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO9TXL0Y4OHwAAAABJRU5ErkJggg==";
let bytes = Utilities.base64Decode(data);
let ssblob = Utilities.newBlob(bytes, "image/png", "yourImage");
Logger.log(bytes.length);
Logger.log(ssblob.getName());
Logger.log(ssblob.getDataAsString());
Logger.log( ssblob.getContentType());
var ss = SpreadsheetApp.getActiveSheet();
ss.insertImage(ssblob,4,4);
}