Image Vs Css

Using IMG tags adds weight to your files and if such files are heavy, you are in for double trouble. Using CSS for images, typically only works for backgrounds.

I say if you need a background, declare in the CSS otherwise, use an IMG tag in the HTML.

Having said that, though redundant, there is nothing wrong with you creating IMG tags in your HTML like so:
<img src="whateversource" id="headImg" /> then having in your CSS:
img#headImg {
    width: 30px;
    height: 30px;
    border: 0;
}

though IMHO, after a while, you might end up with bulky CSS files doing this.  I personally only use this approach if I have a bunch of images that share teh same dimensions and behaviours and in that case, I would use class not ID.

Adding to all contributed so far, the technique still entails coding smartly. Pages loading faster with CSS in an advantage so using the <img> tag and controlling attributes with CSS is preferable.