Placing an image under another image

Question

HI, I am freelancer and got my first major project. For my client, I have to develop a website using asp.net and C#, where in one page, when the user uploads a image, the images has to be placed under the clock image. I am able to place an image over another image(like photo on T-Shirt), but I am unable to accomplish this one. Yesterday when I went to the following link, http://www.cafepress.com/cp/customize/product.aspx?clear=true&no=49 they did exactly what I am trying to do. Can u please help how to implement the above one. Seeking your help. Regards, Swami