Hi,
Do you have the issue with other emails (like the ones sent to the customer) ? You can check them in the menu Customers>Emails history.
The main images ( the header and footer) are located in the media/com_hikashop/images/mail/ folder. So please check that folder via FTP.
If the files are there and they don't appear in the emails, it means that you have some configuration issue on your web server fobidding it to serve the files in that folder (for example with a customized htaccess)
If the files are really not there, then it's likely you have a permission issue on one of the folders which prevented the Joomla installer from adding the files there during the installation process. You could check the permissions via FTP and once fixed, install again the install package of HikaShop. A simpler solution would be to extract the files of the install package on your local computer and manually upload the files from the install package to the correct folder via FTP.
I personally think that all the images are were they should be and it is a web server configuration issue. Because you also have the issue with the thumbnails of the products on your screenshot and these are generated on the fly, so folder permissions should not be a problem for them.