If I'm reading your question (and HTML) right, you're creating (as esteemed monk merlyn points out) a dumbnail. Please don't let the browser resize your image. It will generally not look as good as an actual image resize and you'll be wasting bandwidth downloading a larger image than you want.
in reply to Can't automaticaly HTML-resize my images
A good strategy is to pre-size your images to 3 or 4 standard sizes and then send the image you want. It's quite easy to to use something like Image::Magick to resize your images (in ratio) as you add images.