Thank you for your answer, but I still can't get it to work. My GetImageNames looks like this:

public static List<string> GetImageNames()
    {
        string imgPath = PhysicalApplicationPath +"/Images/";
        List<string> images = new List<string>();
        
        DirectoryInfo directoryInfo = new DirectoryInfo(imgPath);

        FileInfo[] fileInfo = directoryInfo.GetFiles();

        
        for (int i = 0; i < fileInfo.Length; i++)
        {
            images.Add(fileInfo[i].Name);
        }
        return images;
  
     }