var fd = new OpenFileDialog
{
    Multiselect = true,
    Title = "Open Image",
    Filter = "Image|*.jpg"
};

using (fd)
{
    if (fd.ShowDialog() == DialogResult.OK)
    {
       int i = 1;
       foreach (String file in fd.FileNames)
       {
           if (i <= 10) {
               i++;
               Console.WriteLine(i + ";" + file);
               Task task = new Task(() =>
               {
                   // do some stuff
               });
               task.Start();
           }
           else
           {
               Task.WaitAll();
               i = 1;
           }
       }
    }
}
Console.WriteLine("Wait for Tasks");
Task.WaitAll();
Console.WriteLine("Waited);