mask over the image

I would like to create a mask image to round off the bottom and put under a shadow. How do I add the mask over the image?
thanks

Hi, there is at least two solutions to do that, one of them is very easy and compatibility with all browsers even old one. You've to prepare 3 images for slideshow in photoshop, where you add curves and shadows. Than use slideshow module and in css change position of dots * * *

Actually wanted to keep the images in their original format, automatically applying a mask over. is it possible?

solved!
I used the style Appproteach and I replaced the image with the mask I created with photosop.
I fixed the css and everything works:
http://wwwtest.minervaresort.it/

Now we can upload rectangular images and the mask will create the effect rounded with the shadow down.