Possible reasons

• the CSS of your Joomla template might influence the image size. Most likely is a template which sets the height of an image to auto !important. This will never work. Just remove the !important. While this is hidden sometimes in the templates CSS files there is a chance that you can turn this off in the options of your template.

  Common CSS issue screen shot.

• Your images are too small to spread to the necessary width

• You uploaded your images using FTP? You used the Sync Database process? Make sure you hit the Sync Files button to load the image metadate into the database.