public File getRandomContainerPNG() {
        File dir = new File(MainClass.CONTAINERS_DIR);

        if (!dir.exists()) {
            dir.mkdir();
        }

        if (!dir.exists() || !dir.isDirectory()) {
            return null;
        }

        File[] files = dir.listFiles(new FilenameFilter() {
            @Override
            public boolean accept(File directory, String fileName) {
                return fileName.toLowerCase().endsWith(".png");
            }
        });

        Random r = new Random(System.currentTimeMillis());

        if (files.length > 0) {
            return files[r.nextInt(files.length)];
        }

        return null;
    }