title: How to enable caching of background images in ruby on rails?
body: <p>How can I cache background images (forcefully) in user's browser. 
  It will great to set a expiry time of 1 week or 1 month something.</p>
  
  <p><em>PS:I have a page which shows listing based upon category. Every category has its own background image and I want to cache those background images.Every image is something about 20-30kb and I have some 20 categories.</em> </p>