The way an email appears when printed is decided by the recipient's email provider and the printer settings. 
If you would like to share an image that recipients can easily print, you might consider inserting a link to a PDF file in the email and advising recipients to print from that link. If you would like the image or flyer visible in the email, you can add the PDF hyperlink to the image and advise recipients to click on the image for a printable version.

MakeUseOf's Everything You Need To Know About Printing Emails
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