🚀 go-pugleaf

That works, but I don't like the idea of changing the files in any way, even if the added pixels are "almost" transparent. ....So I came up with the following:

_____________________________________________________________

//////////////////////////////////////////////////////////////////////////////////////////////////
app.preferences.rulerUnits = Units.PIXELS;
app.preferences.typeUnits = TypeUnits.PIXELS;
//////////////////////////////////////////////////////////////////////////////////////////////////

selectedFolder = Folder.selectDialog( "Please select input folder");

var fileList = selectedFolder.getFiles();
for(var aFile = 0; aFile<fileList.length;aFile++){ 	var file = fileList[aFile]; 	if(file instanceof File && file.name.match(/\.(jpg|tif|gif|png)$/i)){

		open(file);

		////////////////////////////////////////Add Extra Boarder Stripe to maintain relative positon
		var Width =activeDocument.width.value;
		var Height =activeDocument.height.value;
		activeDocument.resizeCanvas(Width+2, Height, AnchorPosition.MIDDLECENTER)
		var Width =activeDocument.width.value;
		var Height =activeDocument.height.value;
		var fillColor = new SolidColor;
		fillColor.rgb.hexValue = '000000';
		activeDocument.selection.select([[0,0],[1,0],[1,Height],[0,Height]], SelectionType.REPLACE, 0, false);
		activeDocument.selection.fill(fillColor, ColorBlendMode.NORMAL, 100, false );
		activeDocument.selection.deselect();
		activeDocument.selection.select([[(Width-1),0],[Width,0],[Width,Height],[(Width-1),Height]], SelectionType.REPLACE, 0, false);
		activeDocument.selection.fill(fillColor, ColorBlendMode.NORMAL, 100, false );
		activeDocument.selection.deselect();
		////////////////////////////////////////

		if(documents.length > 1){

			////////////////////////////////////////Add to Frame Strip
			activeDocument.selection.selectAll();
			activeDocument.selection.copy();
			activeDocument.close(SaveOptions.DONOTSAVECHANGES);
			activeDocument = documents[0];
			app.activeDocument.resizeCanvas(app.activeDocument.width,app.activeDocument.height+Height, AnchorPosition.TOPCENTER);
			activeDocument.paste();
			activeDocument.selection.selectAll();
			align('AdBt');
			app.activeDocument.selection.deselect();
			activeDocument.mergeVisibleLayers();
			////////////////////////////////////////
		}

	}else{
		continue;
	}
}

////////////////////////////////////////Remove Extra Boarder Stripe and Save
var Width =activeDocument.width.value;
var Height =activeDocument.height.value;
activeDocument.resizeCanvas(Width-2, Height, AnchorPosition.MIDDLECENTER)









//////////////////////////////////////////////////////////////////////////////////////////////////
//CUSTOM FUNCTIONS
//////////////////////////////////////////////////////////////////////////////////////////////////

function align(method) {
   var desc = new ActionDescriptor();
   var ref = new ActionReference();
   		ref.putEnumerated( charIDToTypeID( "Lyr " ), charIDToTypeID( "Ordn" ), charIDToTypeID( "Trgt" ) );
   		desc.putReference( charIDToTypeID( "null" ), ref );
   		desc.putEnumerated( charIDToTypeID( "Usng" ), charIDToTypeID( "ADSt" ), charIDToTypeID( method ) );
   executeAction( charIDToTypeID( "Algn" ), desc, DialogModes.NO );
};