You have this in your CSS:
border: medium none;
The height: auto is over-riding the declared height on your images. Remove this and they will display at the sizes declared. Then you'll have a different problem, because the declared sizes do not scale proportionally to the original image, and your images will appear distorted.
If you need an image to appear in a 150px by 75px box, and the original image does not have a 2:1 aspect ratio (e.g. 400px x 200px) then I don't see you have much option but to edit the image. You could just declare the height and let the image scale, but in the case of the second one, that will leave you with a small square image instead.
irishman is referring to resizing images here. Ideally, you reduce the image to the size at which you want it to display and then declare both width and height.