As above. The issue is, that when using getSkinUrl in Magento to plonk an image anywhere, if you also use SSL, on the https:// versions of the page, you sometimes (not always!) get a NON secure image.
i.e. and chrome dont like this one bit. They'll warn the customer that you're totally unsafe, and shouldn't be trusted. Hmm. A bit extreme, to say the least.
The solution is, well, the reason first. getSkinUrl seems to be caching the images in question. So the solution is to tell it to refresh that image.
I can't say I understand this 100%, but I took it from here (in the comments):
file to edit:
app/code/local/Mage/Catalog/Block/Navigation.php
(if you dont have the above, copy it from app/code/core - NEVER edit core files, always copy them over to app/code/local)
line to add (in magento 1.6 at least!) :
public function getCacheKeyInfo()
{
$shortCacheId = array(
'CATALOG_NAVIGATION',
Mage::app()->getStore()->getId(),
Mage::getDesign()->getPackageName(),
Mage::getDesign()->getTheme('template'),
Mage::getSingleton('customer/session')->getCustomerGroupId(),
'template' => $this->getTemplate(),
'name' => $this->getNameInLayout(),
$this->getCurrenCategoryKey(),
$this->getSkinUrl()
);
$cacheId = $shortCacheId;
$shortCacheId = array_values($shortCacheId);
$shortCacheId = implode('|', $shortCacheId);
$shortCacheId = md5($shortCacheId);
$cacheId['category_path'] = $this->getCurrenCategoryKey();
$cacheId['short_cache_id'] = $shortCacheId;
return $cacheId;
}