Consider using a CDN network such as Rackspace or Amazon, storing images on these types of networks are super fast since your images will be mirrored all over the globe and ultimately improve your page load time which in turn improves your SEO.
CDN networks are pay as you go and cost very little to run and they are super easy to use... just like dropbox if you used that before, or you can even download plugins for WordPress / Joomla / Drupal which integrate direct upload options.
CDN networks don't have send limits, or storage limits since you pay for your usage. Rackspace for example charge around 12p per a GB per a month for storage and less for sending. Worth considering if you want your site super fast.