imres.js

var ImageResize = {
  margin: 8,
  
  parse: function(css_id, margin) {
    if(margin) { this.margin = margin; }
    
    $$('#' + css_id + ' img').each(function(img) { 
      this.resize(img, $(css_id).getWidth() - this.margin); 
    }, this);    
  },
  
  resize: function(img, max_width) {
    // if image is bigger that max_width we add them width = max_width and don't check image again
    if (img.width > max_width) {
      img.style.width = max_width + 'px';
      return true;
    }
    
    // if image isn't complete loaded just bind to check size again after 5 ms
    if (!img.complete) {
      setTimeout(function() { 
        ImageResize.resize(img, max_width); 
      }, 5);
    }
    return false; 
  }
}