Drupal 7 have a very useful image-formatting tool which automatically renders images at a predefined resolution. In other words, for source images uploaded in an image field, the image format can create image derivatives at the resolution specified in the format, leaving the source image intact. If the source image is then modified, the derivative images are reconstructed as needed.
For example, you might want to always display a user's profile picture at a particular resolution on their profile. Using an image format, you can guarantee that whatever image the user uploads, the profile picture will be at the resolution you want.
In this recipe, we will be creating a new image format for the Article content type and applying it so that all images displayed in the article's node view are rendered at 150x50 pixels.