For those looking for a fix for this issue, the culprit is a single line in one template file. For my client, the file and line of code were as follows. Yours may be slightly different depending on your configuration, but hopefully this will give you a way to approach the problem.
File: wp-content/plugins/woocommerce/includes/abstracts/abstract-wc-product.php
Line: line 1735.
return str_replace( array( ‘https://’, ‘http://’ ), ‘//’, $image );
I edited this to the following, making as small a change as possible:
return str_replace( array( ‘https://’, ‘http://’ ), ‘http://’, $image );
The shopping cart element now renders the thumbnail with a full URL, which gets passed into the quote email.
Note that if your implementation enforces https, you may need to change the prefix. This code exists, I imagine, to standardise the protocol for the images to whatever is in use in any installation, but as we’ve seen it breaks third-party integration when it drops the image into an email.
Hope this helps.
