How to make product feed output HTTPS links to image URLs?
To include an HTTPS link to an image URL in a product feed, please open app/code/local/Amasty/Feed/Model/Profile.php.
Then find the #344 line and comment out:
$value = str_replace('https:', 'http:', $mediaConfig→getMediaUrl($value)).
After you save changes, flush Magento cache and generate the feed once again.