Crude Photoshop script to import a series of images and lay them out into a sprite sheet.

sprites.jsx

const FRAME_WIDTH  = 410;
const FRAME_HEIGHT = 280;
const MAX_COLUMNS  = 10;

var newDocumentName = prompt("Name of new document?", "New Sprite Sheet");


var images = getFolder(),
    background = getBackground(),
    columns = Math.min(MAX_COLUMNS, images.length),
    rows = Math.ceil(images.length/MAX_COLUMNS),
    docRef = app.documents.add(columns*FRAME_WIDTH, rows*FRAME_HEIGHT, 72, newDocumentName, NewDocumentMode.RGB, DocumentFill.TRANSPARENT, 1);

var bgDoc = app.open(background);
bgDoc.selection.selectAll();
bgDoc.selection.copy();
bgDoc.close(SaveOptions.DONOTSAVECHANGES);

var bgLayers = docRef.layerSets.add();
bgLayers.name = "Background";

for(i=0; i<images.length; i++)
{
    var column = i % MAX_COLUMNS,
        row = Math.floor(i / MAX_COLUMNS);
    
    var h = row*FRAME_HEIGHT,
        v = column*FRAME_WIDTH;
    
    var coord = [
        [v, h],
        [v, h + FRAME_HEIGHT],
        [v + FRAME_WIDTH, h + FRAME_HEIGHT],
        [v + FRAME_WIDTH, h],
        [v, h]
    ];
    
    docRef.selection.select(coord, SelectionType.REPLACE);
    docRef.paste();
}

var fireworksLayers = docRef.layerSets.add();
fireworksLayers.name = "Fireworks";
fireworksLayers.blendMode = BlendMode.LIGHTEN;

for(i=0; i<images.length; i++)
{
    var column = i % MAX_COLUMNS,
        row = Math.floor(i / MAX_COLUMNS);
    
    var imgDoc = app.open(File(images[i])),
        layerName = imgDoc.name;
    
    var solid = new SolidColor();
    solid.rgb.red = 0;
    solid.rgb.green = 0;
    solid.rgb.blue = 0;
    
    var layer = imgDoc.artLayers.add();
    imgDoc.selection.selectAll();
    imgDoc.selection.fill(solid);
    
    imgDoc.layers[0].move(imgDoc.layers[1], ElementPlacement.PLACEAFTER);
    
    imgDoc.flatten();
    imgDoc.selection.selectAll();
    imgDoc.selection.copy();
    imgDoc.close(SaveOptions.DONOTSAVECHANGES);
    
    var h = row*FRAME_HEIGHT,
        v = column*FRAME_WIDTH;
    
    var coord = [
        [v, h],
        [v, h + FRAME_HEIGHT],
        [v + FRAME_WIDTH, h + FRAME_HEIGHT],
        [v + FRAME_WIDTH, h],
        [v, h]
    ];
    
    docRef.selection.select(coord, SelectionType.REPLACE);
    docRef.paste();
    
    docRef.activeLayer.name = layerName;
}

function getBackground(){
    var path = "", image;
    while(true)
    {
        path = prompt("Complete path to source background image:", path);
        if(path)
        {
            image = new File(path);
            return image;
        }
        
        alert("Enter a path!");
    }
}

function getFolder(){
    var folder, path = "", images;
    while(true)
    {
        path = prompt("Complete path to folder holding images:", path);
        if(path)
        {
            folder = new Folder(path);
            images = folder.getFiles("*.png");
            if(images.length > 0)
            {
                images.sort();
                return images;
            }
        }
        
        alert("No images found.");
    }
}