Resizing and Centering Images in Google Docs with Google Apps Script

function resizeAndCenterImages() {
  // Open the document by ID. Replace with your document ID.
  var docId = 'YOUR_DOCUMENT_ID_HERE';
  var doc = DocumentApp.openById(docId);
  var body = doc.getBody();
  
  // Get the page width in points
  var pageWidth = doc.getPageWidth();
  var maxImageWidth = pageWidth * 0.75;

  // Get all the elements in the document
  var totalElements = body.getNumChildren();
  
  for (var i = 0; i < totalElements; i++) {
    var element = body.getChild(i);
    
    if (element.getType() == DocumentApp.ElementType.PARAGRAPH) {
      var paragraph = element.asParagraph();
      var numChildren = paragraph.getNumChildren();
      
      for (var j = 0; j < numChildren; j++) {
        var child = paragraph.getChild(j);
        
        if (child.getType() == DocumentApp.ElementType.INLINE_IMAGE) {
          var image = child.asInlineImage();
          var originalWidth = image.getWidth();
          var originalHeight = image.getHeight();
          
          // Calculate the new dimensions maintaining the aspect ratio
          var newWidth = maxImageWidth;
          var newHeight = (newWidth / originalWidth) * originalHeight;
          
          // Resize the image
          image.setWidth(newWidth);
          image.setHeight(newHeight);
          
          // Center the image by wrapping it in a centered paragraph
          paragraph.removeChild(image);
          var centeredParagraph = body.insertParagraph(i + 1, "");
          centeredParagraph.appendInlineImage(image);
          centeredParagraph.setAlignment(DocumentApp.HorizontalAlignment.CENTER);
          i++;  // Adjust index to account for newly inserted paragraph
          break;  // Exit inner loop after processing the image
        }
      }
    }
  }
}