Automatically placing Images(18) from a file into frames (18).

Assuming they are always the same aspect ratio and you have autofitting configured in your template, and placement location doesn't matter, then this should work: 

var afs = File.openDialog("Choose all the photos", "*", true);
try { var doc = app.activeDocument; } catch(e) { exit(); } 
var apis = doc.allPageItems;
var n = apis.length;
var i = 0;
if (n !== afs.length) { alert("Number of files selected doesn't match rectangles on page. Placing as much as we can."); }
for (i; i < n; i++) {
    try { 
        apis[i].place(afs[i]);
    } catch(e) {}
}