Add the following to list.phtm:
//$_productCollection=$this->getLoadedProductCollection();
$_productCollection = clone $this->getLoadedProductCollection();
$_productCollection->clear()
->addAttributeToFilter('small_image', array('neq' => 'no_selection'))
->load();
This answer recommended the following:
->addAttributeToFilter('image', array('neq' => 'no_selection'))
Whereas I have set it to:
->addAttributeToFilter('small_image', array('neq' => 'no_selection'))
The reason the previous answer did not work was because the product collection doesn't load the regular image, and therefore the regular image cannot be added as an attribute to filter, so instead, I added the small_image as the attribute to filter.
You can also try R.S's answer where he adds the image to the page and hence the collection. You may have to also add all attributes using:
->addAttributeToSelect('*')