resizing proportionaly

Hello, I’m beginner in these wanderings, just know a little html and css and no php.
Use the theme ChicTheme, such as “magazine”, which puts an emphasis on photos of posts. The images are automatically resized but not proportionally, something that, as a photographer, I do not want. I tried to put the photos with other dimensions, but still no luck. Must be something in php that always resize that window. I have also tried to resize the window (which has the proportions of a photo), but … nothing! My site: http://www.barrento.com/wordpress/
I find it strange that all type of “newspaper” or “magazine” like themes that I found do not have the “featured” with the same portion of a typical picture: does someone here knows a theme that does not resize pictures, or resize then proportionally?
I hope to receive some feedback here, Thank you.