Magento 1.9.2.3 – Get Category Image to Front-End from Custom Attribute

I'm doing it in phtml file like this way

<?php $categories = Mage::getModel('catalog/category')->getCollection()->addAttributeToSelect('*'); ?>

<?php foreach ($categories as $category): ?>
   <?php $categorySku = $category->getCategory_sku(); ?>
   <?php print_r ($categorySku); ?>
<?php endforeach; ?>

That way I can populate all my custom category attribute values which is category_sku :).

And this will make it to a select option list.

    <?php $categories = Mage::getModel('catalog/category')->getCollection()->addAttributeToSelect('*'); ?>

        <select id="my-id" name="my-name">
            <option value="">Select</option>
            <?php foreach ($categories as $category): ?>
<?php /*magento fetch data by using get and attibute name like banner_id change to getBannerId*/   ?>
                <?php $categorySku = $category->getCategorySku(); ?>
                <option value="<?php echo $categorySku; ?>"><?php echo $categorySku; ?></option>
            <?php endforeach; ?>
        </select>

Expanding on @TimVroom's answer please use store emulation in favor of changing the currentStore or setting the isSecureArea. You can read more about emulation on the Inchoo blog.

class Mynamespace_Mymodule_SetmyattributeController extends Mage_Core_Controller_Front_Action 
{        

    public function indexAction() 
    {

        $categoryId = $this->getRequest()->getParam('id'); // Get id from params (1)

        // start emulation
        $appEmulation = Mage::getSingleton('core/app_emulation');
        $initialEnvironmentInfo = $appEmulation->startEnvironmentEmulation(0);


        $category = Mage::getModel('catalog/category')->load($categoryId); // Load category (loads fine)
        $category->setMyattribute(0); // <-- set Attribute
        $category->save(); // <-- save the category


        // stop, return to origional env.
        $appEmulation->stopEnvironmentEmulation($initialEnvironmentInfo);

        /** Re-index the products and category EAV **/
        $process = Mage::getModel('index/process')->load(5); $process->reindexAll();  // Re-index category EAV
        $process = Mage::getModel('index/process')->load(6); $process->reindexAll();  // Re-index Category Products

        echo Mage::helper('core')->jsonEncode(array('status'=>'success'));

        exit;
    }

}