I think you may re-scaling them in the browser by adding a style of “height:100%; width:100%" to the <img> tag.
If I look at the raw images, they are in the correct proportions. For example: http://56.media.tumblr.com/c3138893834bd8660d1f795e436a630f/tumblr_nzibfhiwE31v1683uo1_500.jpg