By specifying the height and width in the img-tag, you will not optimize the image quality and image loading speed. The full size image will be loaded over the wire to the browser, then the browser will do the shrinking. It could be get some distortions. It all depends on the client monitor and browser. If you want to resize the image and have good quality images, you need  to find an image editng tool, like fireworks or photoshop. With this kind of tool, you can resize the images with good quality. Then upload the images to your site, the image loading speed will be improved as well.