how to print mirror image

Welcome to the Apple Support Communities!

I understand you would like to print a mirror image. Can you tell us what application or document you are working with and what model printer you are using?
In general, some printers have a setting for mirror printing, specifically if the media type is set to T-shirt Transfer or something similar.
In the Preview app, you can flip an image horizontally to get a "mirrored" effect.
In word processing documents, make sure the image is by itself and not "in line" with other text. Then you can usually select the image and from the Menu bar choose something like File > Print > Layout > Flip horizontally.
If any of these general suggestions don't help you, please provide a little more information about your issue and we'll be glad to help!
Enjoy your day!