releaseAnchoredObject() not a function????

myPicture.constructor.name results in "Rectangle"

myPicture.parent.constructor.name results in "Array"

In the InDesign document, I have paragraphs of text followed by 1 or more paragraphs with 1 image followed by caption text.  So, for example I might have a paragraph of text followed by another paragraph with an in-line image and some caption text, then another paragraph with an in-line image and some caption text, and then a third.

I'm trying to unanchor the image, group it with a caption text box and then anchor the group to the end of the paragraph before the series of images.  Any ideas?

Here's the code I'm working with so far:  (everything works up until the releaseAnchoredObject line near the end)

//add the indexOf method
if (typeof Array.prototype.indexOf != "function") {  
    Array.prototype.indexOf = function (el) {  
        for(var i = 0; i < this.length; i++) if(el === this) return i;  
        return -1;  
        }  
}  
imageCollection = app.activeDocument.stories.everyItem().rectangles;
imageInsertionPoints = imageCollection.everyItem().parent;
var imageIndexes =[];
for (i=0;i<imageInsertionPoints.length;i++)
{
imageIndexes.push(imageInsertionPoints.paragraphs[0].index);
}
paragraphIndexes = app.activeDocument.stories.everyItem().paragraphs.everyItem().index; 
var imageParagraphIndexes = [];
//find the imageIndexes in the paragraphIndexes array and save their indexes
for (i=0; i<imageIndexes.length; i++)
{
imageParagraphIndexes.push(paragraphIndexes.indexOf(imageIndexes));
}
//create a imageGroupSize array where the length is the number of image groups and each element is the number of images in the group
imageGroupCounter=1;
indexDiff = 0;
var imageGroupSizes = [];
for (i=0;i<imageParagraphIndexes.length-1;i++)
{
indexDiff = imageParagraphIndexes[i+1]-imageParagraphIndexes;
    if (indexDiff == 1)
{
imageGroupCounter++;
     }
else
{
        imageGroupSizes.push(imageGroupCounter);
        imageGroupCounter=1;
}
}
imageGroupSizes.push(imageGroupCounter);
imageIndex = 0;
var myCaption;
for (i=0;i<imageGroupSizes.length;i++)  //for each image group
{
for (j=0;j<imageGroupSizes;j++)  //for each image in the image group
{
captionContent = (app.activeDocument.stories.everyItem().paragraphs[imageParagraphIndexes[imageIndex+j]].contents[0].slice(1)); //grab the caption text  <<-This line has problems
//set up the caption
myPicture = imageCollection[imageIndex+j];
gb = myPicture.geometricBounds[0];
      myCaption = app.activeDocument.textFrames.add();   
  myCaption.properties =  
  {
  geometricBounds : [gb[2],gb[1],gb[2]+2,gb[3]],
  strokeWidth : 0,
  fillColor : "None",  
  contents : captionContent
  };  
myPicture.parent[0].anchoredObjectSettings.releaseAnchoredObject(); //<--this line doesn't work
// myPicture.parent.groups.add([myPicture, myCaption])
// anchor the group at the end of the paragraph before the image group
  // delete the caption text from the paragraph
// delete the paragraph that originally contained the image and caption text
}
imageIndex+=j;
}

How can I tell what version of the DOM I am using?