title: Upload different image sizes or a single size to be processed later?
body: <p>My website allows users to upload profile images, which are then represented in several (about 3 or 4) different sizes around the site.</p>
  
  <p>As the site grows, there is always the possibility that the image sizes will need to be tweaked, or new image sizes will be needed later.</p>
  
  <p>How does a site like Facebook or Twitter handle this? Do they process the image into different sizes right at the upload time, or do they store higher quality images and process them server-side when needed?</p>
  
  <p>Is there a common way to handle this?</p>