Problem with Gallery Image Dimensions

This is a post from my blog
http://www.demortalz.com/2011/11/21/mind-blowing-hd-wallpapers/

and this is a post from another blog
http://crispme.com/showcase-the-finest-architecture-by-muslims-1/

now the problem is, all of his pictures are of 450 x 250, while my pictures are some 450 x 250 and some are smaller in size. This is because on his blog, the thumbnail is cropped from the picture if its dimensions are irregular.
HOw do I do that in my blog?

PLEASE HELP!