How to change color swatch of colored greyscale pictures using ExtendScript in InDesign?

I've got the following problem/situation:

12-page document (ID CC 2015)
one frame with a greyscale picture per page
the pictures are colored with the same color swatch (e.g. "universal") on all pages (white arrow, applied color swatch)

What I want to do now, is to write a script to color every picture with a different color swatch, e.g. the picture on page 1 with color swatch "1", the picture on page 2 with color swatch "2" etc. But I don't know how to access the picture itself (instead of the frame) and change its color. Is this even possible?

Thanks in advance.

Solution

This should do the trick. It currently sets random color for the images and only looks for rectangles. You could use

page.allPageItems

instead. (if you also have images in ovals or polygons)

// the main function
var main = function() {
  var doc = app.activeDocument; // get the current document
  // loop the pages
  for (var i = 0; i < doc.pages.length; i++) { 
    var page = doc.pages[i]; // isolate the page
    // loop all rectangles
    for(var j = 0; j < page.rectangles.length;j++){
      var rect = page.rectangles[j]; // isolate a rectangle
      // test if there is an image inside
      if(rect.images.length > 0){
        var image = rect.images[0]; // isolate the image
        // asign a random color from th swatches
        image.fillColor = doc.swatches[Math.floor(Math.random()* doc.swatches.length -1)];
      } // end if image
    } // end loop j rectangles
  } // end loop i pages
} // end of main
main(); // run it