Image Styles are preset image treatments that are applied to an image that exists inside your Drupal site.
Perhaps you have something like a Profile feature for members of your department. You have a headshot photo of each member that you want to use both in a large format on their individual profile and in a smaller format on a list of all site members.
If you really wanted to, you could go in and create copies of all of your member's photos and then resize all of those photos down to fit your small photo requirement. Then you could upload both sets of photos to your website and (maybe) manage this doubled set. This isn't too terrible...if you only have five to ten people.
Say you had 100 people in your department, though. That's a fairly substantial size. Additionally, as you're manually processing through all of these photos you will run into issues that will serve to frustrate you even more.
What if you had a way to tell all these photos to just show themselves smaller than what they actually are?
Well, you do have a way to do this. Read on to find out more...