I thought that this answer might be useful for understanding for resolving your issue. Auto Transfer Google sheet generated QR code to Google Doc as Image When the script of this answer is reflected in your showing script, how about the following modification?

Unfortunately, I cannot know your actual script. So, this is a simple modification. Please reflect this in your actual script.

Modified script:

Please add the following function to your script.

// ref: https://stackoverflow.com/a/71151203/7108653
var replaceTextToImage = function (body, searchText, url, width = 200) {
  var next = body.findText(searchText);
  if (!next) return;
  var r = next.getElement();
  r.asText().setText("");
  var img = r.getParent().asParagraph().insertInlineImage(0, UrlFetchApp.fetch(url).getBlob());
  if (width && typeof width == "number") {
    var w = img.getWidth();
    var h = img.getHeight();
    img.setWidth(width);
    img.setHeight(width * h / w);
  }
  return next;
};

And, please modify your script as follows.

From:

newFileBody.replaceText('<<emp-sign>>', emp_sign);
newFileBody.replaceText('<<it-sign>>', it_sign);

To:

replaceTextToImage(newFileBody, '<<emp-sign>>', emp_sign);
replaceTextToImage(newFileBody, '<<it-sign>>', it_sign);

Note:

• From your showing images, I guessed that in your situation, var emp_sign = data[i][11] and var it_sign = data[i][12] are the image URLs. Also, it supposes that the files of your URLs are publicly shared, and your URLs can be directly accessed to the images. Please be careful about this.
• If you want to change the image size, please add the image width to the 4th argument of the function replaceTextToImage.
• If you use my modification to your script and the script doesn't work, please provide your whole script. I would like to confirm it.