an image that is inside the content
The $content variable is an array (a 'render' array in Drupal parlance). You'll be able to render the parts of the content individually instead of all in one go if you want, and wrap them in specific HTML:

&lt;div class="body"&gt;
  &lt;?php echo render($content['body']); ?&gt;
&lt;/div&gt;

&lt;div class="some-image-field"&gt;
  &lt;?php echo render($content['field_some_image_field']); ?&gt;
&lt;/div&gt;


You can even provide a template file for just the content type you want to change, by calling it node--content-type-name.tpl.php, and just apply the changes to that particular content type.

For styling, each field will already be wrapped in HTML with many, many classes attached to it. Just fire up developer tools/firebug, inspect the elements, and you'll find the correct selectors to target with CSS. If that fails, you've can add the wrappers in yourself like in the code example above.