Hello
...or you can integrate some javascript zoom plugin with your custom content template.
Seblod upload image field will manage the image upload and the thumbnail creation.
For zoom feature, you should look for some javascript plugin you like
http://www.elevateweb.co.uk/image-zoom/examples
The implementation is usually quite simple and well documented.
You will probably need to load some required javascript and CSS files. You can do it in your custom template
$doc = JFactory::getDocument();
$doc->addStyleSheet('/path/to/style.css');<br>
$doc->addScript('path/to/script.js');
View the page source and check if the files are in the of your page.
If yes, follow the instruction in the plugin documentation (copy & paste from HTML example to your template).
You will probably need to mention the URL to your image thumbnail and large image. You'll find both in your Seblod image field
<?php echo $cck->get( 'your_image' )->thumb1; ?>
<?php echo $cck->get( 'your_image' )->value; ?>
Hope it helps
Michal