crow,
does it not work to just stick down to the metal w/ modpodge?
you can use image transfer solution (need to reverse your image though) in that case the white part of image will show the metal after you remove the paper.
http://www.sherrihaab-shop.com/craft-supplies/image-transfer-its.htmli'm not sure if the color would be affected by alcohol, might still need varnish
btw, i looked at your shop to see what you meant by 'flask', you might want to read up on copyright law, some of your images might be copyright protected
dover publications is good source for copyright free images