Image styles are a great tool for working with images in your content, and it comes as part of Drupal 7 core. Drupal generates images for you using pre-built image styles as well as ones that you create. This means that you don't necessarily have to precisely resize an image before uploading it to your Drupal site. This series starts out with the basics of what image styles are and how you can use them, moves on to show some cool tricks, and then finishes up by showing how you preserve all that hard work and re-use it elsewhere.
I am going to show you how you can upload an image of any size and it will automatically display as the size/style that you designate by editing the display field settings for your content type. We are going to add an image field to the basic page content type and set the node display to use medium size of 220 wide by 220 tall. Being able to set a standard for image display creates consistency and a better user experience. Site builders and content administrators will also have less work because you don’t need to cut all of you images before you upload them. Drupal does all the work for you!